diff --git a/Cargo.lock b/Cargo.lock
index 02e6177..5714db7 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -10,6 +10,7 @@ dependencies = [
  "clap",
  "config",
  "daemonize",
+ "nom",
  "serde",
  "serde_derive",
  "syslog-tracing",
diff --git a/Cargo.toml b/Cargo.toml
index 24f9063..ae5902b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -26,6 +26,7 @@ anyhow = { version = "1.0.94", default-features = false, features = ["std"] }
 clap = { version = "4.5.23", default-features = false, features = ["color", "derive", "help", "std", "string"] }
 config = { version = "0.14.0", default-features = false, features = ["toml"] }
 daemonize = { version = "0.5.0", default-features = false }
+nom = { version = "7.1.3", default-features = false }
 serde = { version = "1.0.216", default-features = false, features = ["std"] }
 serde_derive = { version = "1.0.216", default-features = false }
 syslog-tracing = { version = "0.3.1", default-features = false }
diff --git a/src/config.rs b/src/config.rs
index 2219371..e4457cf 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -1,5 +1,6 @@
 mod account;
 mod certificate;
+mod duration;
 mod endpoint;
 mod global;
 mod hook;
@@ -7,6 +8,7 @@ mod rate_limit;
 
 pub use account::*;
 pub use certificate::*;
+pub use duration::*;
 pub use endpoint::*;
 pub use global::*;
 pub use hook::*;
diff --git a/src/config/certificate.rs b/src/config/certificate.rs
index 168043a..77fd54d 100644
--- a/src/config/certificate.rs
+++ b/src/config/certificate.rs
@@ -1,3 +1,4 @@
+use crate::config::Duration;
 use anyhow::Result;
 use serde::{de, Deserialize, Deserializer};
 use serde_derive::Deserialize;
@@ -24,8 +25,8 @@ pub struct Certificate {
 	#[serde(default)]
 	pub(in crate::config) kp_reuse: bool,
 	pub(in crate::config) name: Option<String>,
-	pub(in crate::config) random_early_renew: Option<String>,
-	pub(in crate::config) renew_delay: Option<String>,
+	pub(in crate::config) random_early_renew: Option<Duration>,
+	pub(in crate::config) renew_delay: Option<Duration>,
 	#[serde(default)]
 	pub(in crate::config) subject_attributes: SubjectAttributes,
 }
@@ -214,8 +215,8 @@ subject_attributes.organization_name = "ACME Inc."
 		assert_eq!(c.key_type, KeyType::EcDsaP256);
 		assert_eq!(c.kp_reuse, true);
 		assert_eq!(c.name, Some("test".to_string()));
-		assert_eq!(c.random_early_renew, Some("1d".to_string()));
-		assert_eq!(c.renew_delay, Some("30d".to_string()));
+		assert_eq!(c.random_early_renew, Some(Duration::from_days(1)));
+		assert_eq!(c.renew_delay, Some(Duration::from_days(30)));
 		assert_eq!(c.subject_attributes.country_name, Some("FR".to_string()));
 		assert!(c.subject_attributes.generation_qualifier.is_none());
 		assert!(c.subject_attributes.given_name.is_none());
diff --git a/src/config/duration.rs b/src/config/duration.rs
new file mode 100644
index 0000000..250f85f
--- /dev/null
+++ b/src/config/duration.rs
@@ -0,0 +1,125 @@
+use nom::bytes::complete::take_while_m_n;
+use nom::character::complete::digit1;
+use nom::combinator::map_res;
+use nom::multi::fold_many1;
+use nom::IResult;
+use serde::{de, Deserialize, Deserializer};
+
+type StdDuration = std::time::Duration;
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Duration(StdDuration);
+
+impl Duration {
+	pub(in crate::config) fn from_secs(nb_secs: u64) -> Self {
+		Self(std::time::Duration::from_secs(nb_secs))
+	}
+
+	pub(in crate::config) fn from_days(nb_days: u64) -> Self {
+		Self(std::time::Duration::from_secs(nb_days * 24 * 60 * 60))
+	}
+
+	pub(in crate::config) fn get_std(&self) -> StdDuration {
+		self.0
+	}
+}
+
+impl<'de> Deserialize<'de> for Duration {
+	fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+	where
+		D: Deserializer<'de>,
+	{
+		let s = String::deserialize(deserializer)?;
+		let (_, duration) =
+			parse_duration(&s).map_err(|_| de::Error::custom("invalid duration"))?;
+		Ok(duration)
+	}
+}
+
+fn is_duration_chr(c: char) -> bool {
+	c == 's' || c == 'm' || c == 'h' || c == 'd' || c == 'w'
+}
+
+fn get_multiplicator(input: &str) -> IResult<&str, u64> {
+	let (input, nb) = take_while_m_n(1, 1, is_duration_chr)(input)?;
+	let mult = match nb.chars().next() {
+		Some('s') => 1,
+		Some('m') => 60,
+		Some('h') => 3_600,
+		Some('d') => 86_400,
+		Some('w') => 604_800,
+		_ => 0,
+	};
+	Ok((input, mult))
+}
+
+fn get_duration_part(input: &str) -> IResult<&str, StdDuration> {
+	let (input, nb) = map_res(digit1, |s: &str| s.parse::<u64>())(input)?;
+	let (input, mult) = get_multiplicator(input)?;
+	Ok((input, StdDuration::from_secs(nb * mult)))
+}
+
+fn parse_duration(input: &str) -> IResult<&str, Duration> {
+	let (input, std_duration) = fold_many1(
+		get_duration_part,
+		|| StdDuration::new(0, 0),
+		|mut acc: StdDuration, item| {
+			acc += item;
+			acc
+		},
+	)(input)?;
+	Ok((input, Duration(std_duration)))
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn empty_duration() {
+		let res = parse_duration("");
+		assert!(res.is_err());
+	}
+
+	#[test]
+	fn single_second() {
+		let (_, d) = parse_duration("1s").unwrap();
+		assert_eq!(d.get_std(), StdDuration::from_secs(1));
+	}
+
+	#[test]
+	fn single_minute() {
+		let (_, d) = parse_duration("123m").unwrap();
+		assert_eq!(d.get_std(), StdDuration::from_secs(123 * 60));
+	}
+
+	#[test]
+	fn single_hour() {
+		let (_, d) = parse_duration("10h").unwrap();
+		assert_eq!(d.get_std(), StdDuration::from_secs(10 * 60 * 60));
+	}
+
+	#[test]
+	fn single_day() {
+		let (_, d) = parse_duration("3d").unwrap();
+		assert_eq!(d.get_std(), StdDuration::from_secs(3 * 24 * 60 * 60));
+	}
+
+	#[test]
+	fn single_week() {
+		let (_, d) = parse_duration("1w").unwrap();
+		assert_eq!(d.get_std(), StdDuration::from_secs(7 * 24 * 60 * 60));
+	}
+
+	#[test]
+	fn mixed() {
+		let (_, d) = parse_duration("1d42s").unwrap();
+		assert_eq!(d.get_std(), StdDuration::from_secs(24 * 60 * 60 + 42));
+	}
+
+	#[test]
+	fn duplicated() {
+		let (_, d) = parse_duration("40s20h4h2s").unwrap();
+		assert_eq!(d.get_std(), StdDuration::from_secs(24 * 60 * 60 + 42));
+	}
+}
diff --git a/src/config/endpoint.rs b/src/config/endpoint.rs
index 9a55598..7c822f0 100644
--- a/src/config/endpoint.rs
+++ b/src/config/endpoint.rs
@@ -1,3 +1,4 @@
+use crate::config::Duration;
 use serde_derive::Deserialize;
 use std::path::PathBuf;
 
@@ -6,10 +7,10 @@ use std::path::PathBuf;
 pub struct Endpoint {
 	pub(in crate::config) file_name_format: Option<String>,
 	pub(in crate::config) name: String,
-	pub(in crate::config) random_early_renew: Option<String>,
+	pub(in crate::config) random_early_renew: Option<Duration>,
 	#[serde(default)]
 	pub(in crate::config) rate_limits: Vec<String>,
-	pub(in crate::config) renew_delay: Option<String>,
+	pub(in crate::config) renew_delay: Option<Duration>,
 	#[serde(default)]
 	pub(in crate::config) root_certificates: Vec<PathBuf>,
 	#[serde(default)]
@@ -65,9 +66,9 @@ tos_agreed = true
 			Some("{{ key_type }} {{ file_type }} {{ name }}.{{ ext }}".to_string())
 		);
 		assert_eq!(e.name, "test");
-		assert_eq!(e.random_early_renew, Some("1d".to_string()));
+		assert_eq!(e.random_early_renew, Some(Duration::from_days(1)));
 		assert_eq!(e.rate_limits, vec!["rl 1", "rl 2"]);
-		assert_eq!(e.renew_delay, Some("21d".to_string()));
+		assert_eq!(e.renew_delay, Some(Duration::from_days(21)));
 		assert_eq!(e.root_certificates, vec![PathBuf::from("root_cert.pem")]);
 		assert_eq!(e.tos_agreed, true);
 		assert_eq!(e.url, "https://acme-v02.api.example.com/directory");
diff --git a/src/config/global.rs b/src/config/global.rs
index f60d6cb..bf6f9ab 100644
--- a/src/config/global.rs
+++ b/src/config/global.rs
@@ -1,3 +1,4 @@
+use crate::config::Duration;
 use serde_derive::Deserialize;
 use std::collections::HashMap;
 use std::path::PathBuf;
@@ -23,9 +24,9 @@ pub struct GlobalOptions {
 	pub(in crate::config) pk_file_user: Option<String>,
 	#[serde(default = "get_default_pk_file_ext")]
 	pub(in crate::config) pk_file_ext: String,
-	pub(in crate::config) random_early_renew: Option<String>,
+	pub(in crate::config) random_early_renew: Option<Duration>,
 	#[serde(default = "get_default_renew_delay")]
-	pub(in crate::config) renew_delay: String,
+	pub(in crate::config) renew_delay: Duration,
 	#[serde(default)]
 	pub(in crate::config) root_certificates: Vec<PathBuf>,
 }
@@ -63,8 +64,8 @@ fn get_default_pk_file_ext() -> String {
 	"pem".to_string()
 }
 
-fn get_default_renew_delay() -> String {
-	"30d".to_string()
+fn get_default_renew_delay() -> Duration {
+	Duration::from_days(3)
 }
 
 #[cfg(test)]
@@ -135,8 +136,8 @@ root_certificates = ["root_cert.pem"]
 		assert_eq!(go.pk_file_mode, Some(0o644));
 		assert_eq!(go.pk_file_user, Some("acme_test".to_string()));
 		assert_eq!(go.pk_file_ext, "pem.txt");
-		assert_eq!(go.random_early_renew, Some("2d".to_string()));
-		assert_eq!(go.renew_delay, "21d");
+		assert_eq!(go.random_early_renew, Some(Duration::from_days(2)));
+		assert_eq!(go.renew_delay, Duration::from_days(21));
 		assert_eq!(go.root_certificates, vec![PathBuf::from("root_cert.pem")]);
 	}
 }
diff --git a/src/config/rate_limit.rs b/src/config/rate_limit.rs
index ada0e83..f2557aa 100644
--- a/src/config/rate_limit.rs
+++ b/src/config/rate_limit.rs
@@ -1,3 +1,4 @@
+use crate::config::Duration;
 use serde_derive::Deserialize;
 
 #[derive(Clone, Debug, Deserialize)]
@@ -5,7 +6,7 @@ use serde_derive::Deserialize;
 pub struct RateLimit {
 	pub(in crate::config) name: String,
 	pub(in crate::config) number: usize,
-	pub(in crate::config) period: String,
+	pub(in crate::config) period: Duration,
 }
 
 #[cfg(test)]
@@ -30,7 +31,7 @@ period = "20s"
 		let rl: RateLimit = load_str(cfg).unwrap();
 		assert_eq!(rl.name, "test");
 		assert_eq!(rl.number, 20);
-		assert_eq!(rl.period, "20s");
+		assert_eq!(rl.period, Duration::from_secs(20));
 	}
 
 	#[test]