Add my note + add type hint

Author: ben-cutler-tamarin

doc/source/whatsnew/v3.0.0.rst

@@ -1274,6 +1274,7 @@ Other
 - Fixed bug in the :meth:`Series.rank` with object dtype and extremely small float values (:issue:`62036`)
 - Fixed bug where the :class:`DataFrame` constructor misclassified array-like objects with a ``.name`` attribute as :class:`Series` or :class:`Index` (:issue:`61443`)
 - Fixed regression in :meth:`DataFrame.from_records` not initializing subclasses properly (:issue:`57008`)
+- Fixed bug when parsing datetime array formatting  in :func:`_guess_datetime_format_for_array` where the format string was based on the first item and not the entire series of entered dates
 
 .. ***DO NOT USE THIS SECTION***
 

pandas/core/tools/datetimes.py

@@ -129,7 +129,9 @@ class FulldatetimeDict(YearMonthDayDict, total=False):
 # ---------------------------------------------------------------------
 
 
-def _guess_datetime_format_for_array(arr, dayfirst: bool | None = False) -> str | None:
+def _guess_datetime_format_for_array(
+    arr: np.ndarray, dayfirst: bool | None = False
+) -> str | None:
     # Try to guess the format based on the first non-NaN element, return None if can't
     search_start = 0
     allowed_formats = set()