diff --git a/layouts/json/src/lib.rs b/layouts/json/src/lib.rs
index 812f6ea..39f01eb 100644
--- a/layouts/json/src/lib.rs
+++ b/layouts/json/src/lib.rs
@@ -19,7 +19,6 @@
 pub extern crate jiff;
 
 use jiff::Timestamp;
-use jiff::TimestampDisplayWithOffset;
 use jiff::tz::TimeZone;
 use logforth_core::Diagnostic;
 use logforth_core::Error;
@@ -50,14 +49,26 @@ use serde_json::Map;
 ///
 /// let json_layout = JsonLayout::default();
 /// ```
-#[derive(Default, Debug, Clone)]
+#[derive(Debug, Clone)]
 pub struct JsonLayout {
-    tz: Option<TimeZone>,
+    timezone: TimeZone,
+    timestamp_format: Option<fn(Timestamp, &TimeZone) -> String>,
+}
+
+impl Default for JsonLayout {
+    fn default() -> Self {
+        Self {
+            timezone: TimeZone::system(),
+            timestamp_format: None,
+        }
+    }
 }
 
 impl JsonLayout {
     /// Set the timezone for timestamps.
     ///
+    /// Defaults to the system timezone.
+    ///
     /// # Examples
     ///
     /// ```
@@ -67,7 +78,29 @@ impl JsonLayout {
     /// let layout = JsonLayout::default().timezone(TimeZone::UTC);
     /// ```
     pub fn timezone(mut self, tz: TimeZone) -> Self {
-        self.tz = Some(tz);
+        self.timezone = tz;
+        self
+    }
+
+    /// Set a user-defined timestamp format function.
+    ///
+    /// Default to formatting the timestamp with offset as ISO 8601. See the example below.
+    ///
+    /// For other formatting options, refer to the [jiff::fmt::strtime] documentation.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use jiff::Timestamp;
+    /// use jiff::tz::TimeZone;
+    /// use logforth_layout_json::JsonLayout;
+    ///
+    /// // This is equivalent to the default timestamp format.
+    /// let layout = JsonLayout::default()
+    ///     .timestamp_format(|ts, tz| format!("{:.6}", ts.display_with_offset(tz.to_offset(ts))));
+    /// ```
+    pub fn timestamp_format(mut self, format: fn(Timestamp, &TimeZone) -> String) -> Self {
+        self.timestamp_format = Some(format);
         self
     }
 }
@@ -87,10 +120,14 @@ impl Visitor for KvCollector<'_> {
     }
 }
 
+fn default_timestamp_format(ts: Timestamp, tz: &TimeZone) -> String {
+    let offset = tz.to_offset(ts);
+    format!("{:.6}", ts.display_with_offset(offset))
+}
+
 #[derive(Debug, Clone, Serialize)]
 struct RecordLine<'a> {
-    #[serde(serialize_with = "serialize_timestamp")]
-    timestamp: TimestampDisplayWithOffset,
+    timestamp: String,
     level: &'a str,
     target: &'a str,
     file: &'a str,
@@ -102,16 +139,6 @@ struct RecordLine<'a> {
     diags: Map<String, serde_json::Value>,
 }
 
-fn serialize_timestamp<S>(
-    timestamp: &TimestampDisplayWithOffset,
-    serializer: S,
-) -> Result<S::Ok, S::Error>
-where
-    S: serde::Serializer,
-{
-    serializer.collect_str(&format_args!("{timestamp:.6}"))
-}
-
 impl Layout for JsonLayout {
     fn format(&self, record: &Record, diags: &[Box<dyn Diagnostic>]) -> Result<Vec<u8>, Error> {
         let diagnostics = diags;
@@ -119,9 +146,11 @@ impl Layout for JsonLayout {
         // SAFETY: jiff::Timestamp::try_from only fails if the time is out of range, which is
         // very unlikely if the system clock is correct.
         let ts = Timestamp::try_from(record.time()).unwrap();
-        let tz = self.tz.clone().unwrap_or_else(TimeZone::system);
-        let offset = tz.to_offset(ts);
-        let timestamp = ts.display_with_offset(offset);
+        let timestamp = if let Some(format) = self.timestamp_format {
+            format(ts, &self.timezone)
+        } else {
+            default_timestamp_format(ts, &self.timezone)
+        };
 
         let mut kvs = Map::new();
         let mut kvs_visitor = KvCollector { kvs: &mut kvs };
diff --git a/layouts/text/src/lib.rs b/layouts/text/src/lib.rs
index 548ed16..ad1e3d2 100644
--- a/layouts/text/src/lib.rs
+++ b/layouts/text/src/lib.rs
@@ -19,6 +19,8 @@
 pub extern crate colored;
 pub extern crate jiff;
 
+use std::fmt::Write;
+
 use colored::Color;
 use colored::ColoredString;
 use colored::Colorize;
@@ -61,11 +63,23 @@ use logforth_core::record::Record;
 ///
 /// let layout = TextLayout::default();
 /// ```
-#[derive(Debug, Clone, Default)]
+#[derive(Debug, Clone)]
 pub struct TextLayout {
     colors: LevelColor,
     no_color: bool,
-    tz: Option<TimeZone>,
+    timezone: TimeZone,
+    timestamp_format: Option<fn(Timestamp, &TimeZone) -> String>,
+}
+
+impl Default for TextLayout {
+    fn default() -> Self {
+        Self {
+            colors: LevelColor::default(),
+            no_color: false,
+            timezone: TimeZone::system(),
+            timestamp_format: None,
+        }
+    }
 }
 
 impl TextLayout {
@@ -125,6 +139,8 @@ impl TextLayout {
 
     /// Set the timezone for timestamps.
     ///
+    /// Defaults to the system timezone if not set.
+    ///
     /// # Examples
     ///
     /// ```
@@ -134,7 +150,29 @@ impl TextLayout {
     /// let layout = TextLayout::default().timezone(TimeZone::UTC);
     /// ```
     pub fn timezone(mut self, tz: TimeZone) -> Self {
-        self.tz = Some(tz);
+        self.timezone = tz;
+        self
+    }
+
+    /// Set a user-defined timestamp format function.
+    ///
+    /// Default to formatting the timestamp with offset as ISO 8601. See the example below.
+    ///
+    /// For other formatting options, refer to the [jiff::fmt::strtime] documentation.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use jiff::Timestamp;
+    /// use jiff::tz::TimeZone;
+    /// use logforth_layout_text::TextLayout;
+    ///
+    /// // This is equivalent to the default timestamp format.
+    /// let layout = TextLayout::default()
+    ///     .timestamp_format(|ts, tz| format!("{:.6}", ts.display_with_offset(tz.to_offset(ts))));
+    /// ```
+    pub fn timestamp_format(mut self, format: fn(Timestamp, &TimeZone) -> String) -> Self {
+        self.timestamp_format = Some(format);
         self
     }
 
@@ -157,14 +195,21 @@ impl Visitor for KvWriter {
     }
 }
 
+fn default_timestamp_format(ts: Timestamp, tz: &TimeZone) -> String {
+    let offset = tz.to_offset(ts);
+    format!("{:.6}", ts.display_with_offset(offset))
+}
+
 impl Layout for TextLayout {
     fn format(&self, record: &Record, diags: &[Box<dyn Diagnostic>]) -> Result<Vec<u8>, Error> {
         // SAFETY: jiff::Timestamp::try_from only fails if the time is out of range, which is
         // very unlikely if the system clock is correct.
         let ts = Timestamp::try_from(record.time()).unwrap();
-        let tz = self.tz.clone().unwrap_or_else(TimeZone::system);
-        let offset = tz.to_offset(ts);
-        let time = ts.display_with_offset(offset);
+        let time = if let Some(format) = self.timestamp_format {
+            format(ts, &self.timezone)
+        } else {
+            default_timestamp_format(ts, &self.timezone)
+        };
 
         let level = self.format_record_level(record.level());
         let target = record.target();
@@ -172,9 +217,12 @@ impl Layout for TextLayout {
         let line = record.line().unwrap_or_default();
         let message = record.payload();
 
-        let mut visitor = KvWriter {
-            text: format!("{time:.6} {level:>6} {target}: {file}:{line} {message}"),
-        };
+        let mut visitor = KvWriter { text: time };
+        write!(
+            &mut visitor.text,
+            " {level:>6} {target}: {file}:{line} {message}"
+        )
+        .unwrap();
         record.key_values().visit(&mut visitor)?;
         for d in diags {
             d.visit(&mut visitor)?;