ENH: Timestamp.tz_convert support non-nano (#47320)

Author: jbrockmendel

pandas/_libs/tslibs/timestamps.pyx

@@ -2121,8 +2121,6 @@ default 'raise'
         >>> pd.NaT.tz_convert(tz='Asia/Tokyo')
         NaT
         """
-        if self._reso != NPY_FR_ns:
-            raise NotImplementedError(self._reso)
 
         if self.tzinfo is None:
             # tz naive, use tz_localize
@@ -2131,7 +2129,8 @@ default 'raise'
             )
         else:
             # Same UTC timestamp, different time zone
-            out = Timestamp(self.value, tz=tz)
+            tz = maybe_get_tz(tz)
+            out = type(self)._from_value_and_reso(self.value, reso=self._reso, tz=tz)
             if out is not NaT:
                 out._set_freq(self._freq)  # avoid warning in constructor
             return out

pandas/tests/scalar/timestamp/test_timestamp.py

@@ -22,6 +22,7 @@
 from pandas._libs.tslibs.timezones import (
     dateutil_gettz as gettz,
     get_timezone,
+    tz_compare,
 )
 from pandas.errors import OutOfBoundsDatetime
 import pandas.util._test_decorators as td
@@ -763,6 +764,16 @@ def test_month_name(self, dt64, ts):
         alt = Timestamp(dt64)
         assert ts.month_name() == alt.month_name()
 
+    def test_tz_convert(self, ts):
+        ts = Timestamp._from_value_and_reso(ts.value, ts._reso, utc)
+
+        tz = pytz.timezone("US/Pacific")
+        result = ts.tz_convert(tz)
+
+        assert isinstance(result, Timestamp)
+        assert result._reso == ts._reso
+        assert tz_compare(result.tz, tz)
+
     def test_repr(self, dt64, ts):
         alt = Timestamp(dt64)