CLN use pd.Timestamp for single element in converter (#49148)

Author: MarcoGorelli

doc/source/whatsnew/v2.0.0.rst

@@ -258,7 +258,7 @@ Period
 
 Plotting
 ^^^^^^^^
--
+- ``ax.set_xlim`` was sometimes raising ``UserWarning`` which users couldn't address due to ``set_xlim`` not accepting parsing arguments - the converter now uses :func:`Timestamp` instead (:issue:`49148`)
 -
 
 Groupby/resample/rolling

pandas/plotting/_matplotlib/converter.py

@@ -152,9 +152,7 @@ def _to_ordinalf(tm: pydt.time) -> float:
 
 def time2num(d):
     if isinstance(d, str):
-        parsed = tools.to_datetime(d)
-        if not isinstance(parsed, datetime):
-            raise ValueError(f"Could not parse time {d}")
+        parsed = Timestamp(d)
         return _to_ordinalf(parsed.time())
     if isinstance(d, pydt.time):
         return _to_ordinalf(d)