chore: mention that the offset varies based on daylight savings time

datafusion/functions/src/datetime/to_local_time.rs

@@ -296,8 +296,14 @@ impl ToLocalTimeFunc {
 ///
 /// The difference between `1_553_990_400_000_000_000` and `1_553_994_000_000_000_000` is
 /// `3600_000_000_000` ns, which corresponds to 1 hour. This matches with the timezone
-/// offset for "Europe/Brussels". Consequently, DataFusion can represent the timestamp in
-/// local time (with no offset or timezone information) as
+/// offset for "Europe/Brussels" for this date.
+///
+/// Note that the offset varies with daylight savings time (DST), which makes this tricky! For
+/// example, timezone "Europe/Brussels" has a 2-hour offset during DST and a 1-hour offset
+/// when DST ends.
+///
+/// Consequently, DataFusion can represent the timestamp in local time (with no offset or
+/// timezone information) as
 ///
 /// ```text
 /// TimestampNanosecond(Some(1_553_994_000_000_000_000), None)