diff --git a/Cargo.lock b/Cargo.lock
index 3458ffee..de9b0576 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -365,6 +365,7 @@ dependencies = [
  "rustc-hash",
  "tinystr",
  "tzif",
+ "web-time",
 ]
 
 [[package]]
@@ -447,6 +448,16 @@ version = "0.2.95"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "65fc09f10666a9f147042251e0dda9c18f166ff7de300607007e96bdebc1068d"
 
+[[package]]
+name = "web-time"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5a6580f308b1fad9207618087a65c04e7a10bc77e02c8e84e9b00dd4b12fa0bb"
+dependencies = [
+ "js-sys",
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "windows-core"
 version = "0.52.0"
diff --git a/Cargo.toml b/Cargo.toml
index f4f8b62b..7f48f884 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -34,6 +34,9 @@ tzif = { version = "0.2.3", optional = true }
 jiff-tzdb = { version = "0.1.1", optional = true }
 combine = { version = "4.6.7", optional = true }
 
+# System time feature
+web-time = { version = "1.1.0", optional =  true }
+
 [features]
 log = ["dep:log"]
 experimental = ["tzdb"]
diff --git a/src/components/now.rs b/src/components/now.rs
index e35689d5..9d513faf 100644
--- a/src/components/now.rs
+++ b/src/components/now.rs
@@ -35,7 +35,7 @@ impl Now {
 
     pub fn plain_date_time_with_provider(
         tz: Option<TimeZone>,
-        provider: &mut impl TzProvider,
+        provider: &impl TzProvider,
     ) -> TemporalResult<PlainDateTime> {
         let iso = system_date_time(tz, provider)?;
         Ok(PlainDateTime::new_unchecked(iso, Calendar::default()))
@@ -45,7 +45,7 @@ impl Now {
 #[cfg(feature = "std")]
 fn system_date_time(
     tz: Option<TimeZone>,
-    provider: &mut impl TzProvider,
+    provider: &impl TzProvider,
 ) -> TemporalResult<IsoDateTime> {
     // 1. If temporalTimeZoneLike is undefined, then
     // a. Let timeZone be SystemTimeZoneIdentifier().
@@ -69,3 +69,33 @@ fn system_instant() -> TemporalResult<Instant> {
     let nanos = sys::get_system_nanoseconds()?;
     Instant::try_new(i128::from_u128(nanos).temporal_unwrap()?)
 }
+
+#[cfg(test)]
+mod tests {
+    use std::thread;
+    use std::time::Duration as StdDuration;
+
+    use crate::{partial::PartialDuration, tzdb::FsTzdbProvider, Duration, Now};
+
+    #[cfg(feature = "tzdb")]
+    #[test]
+    fn now_datetime_test() {
+        let provider = &FsTzdbProvider::default();
+
+        let now = Now::plain_date_time_with_provider(None, provider).unwrap();
+        thread::sleep(StdDuration::from_secs(2));
+        let then = Now::plain_date_time_with_provider(None, provider).unwrap();
+
+        let two_seconds = Duration::from_partial_duration(PartialDuration {
+            seconds: Some(2.into()),
+            ..Default::default()
+        })
+        .unwrap();
+
+        let now_plus_two = now.add(&two_seconds, None).unwrap();
+
+        assert_eq!(now_plus_two.second(), then.second());
+        assert_eq!(now_plus_two.minute(), then.minute());
+        assert_eq!(now_plus_two.hour(), then.hour());
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 26a64371..35af6674 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -43,7 +43,6 @@
 extern crate alloc;
 extern crate core;
 
-// TODO: Support SystemTime directly / pull in OS code from std::time?
 #[cfg(feature = "std")]
 extern crate std;
 
diff --git a/src/sys.rs b/src/sys.rs
index 6342b2cf..5a074a58 100644
--- a/src/sys.rs
+++ b/src/sys.rs
@@ -2,9 +2,9 @@ use alloc::string::{String, ToString};
 
 use crate::{TemporalError, TemporalResult};
 
-use std::time::{SystemTime, UNIX_EPOCH};
+use web_time::{SystemTime, UNIX_EPOCH};
 
-// TODO: Need to implement system handling for non_std.
+// TODO: Need to implement SystemTime handling for non_std.
 
 /// Returns the system time in nanoseconds.
 pub(crate) fn get_system_nanoseconds() -> TemporalResult<u128> {
diff --git a/src/tzdb.rs b/src/tzdb.rs
index 068988d5..c6e00f48 100644
--- a/src/tzdb.rs
+++ b/src/tzdb.rs
@@ -298,7 +298,9 @@ impl Tzif {
 
 #[inline]
 fn get_local_record(db: &DataBlock, idx: usize) -> LocalTimeTypeRecord {
-    db.local_time_type_records[db.transition_types[idx]]
+    // NOTE: Transition type can be empty. If no transition_type exists,
+    // then use 0 as the default index of local_time_type_records.
+    db.local_time_type_records[db.transition_types.get(idx).copied().unwrap_or(0)]
 }
 
 #[inline]