diff --git a/deepdiff/docstrings/numbers.rst b/deepdiff/docstrings/numbers.rst
index c14fe5ef..ae8d5694 100644
--- a/deepdiff/docstrings/numbers.rst
+++ b/deepdiff/docstrings/numbers.rst
@@ -83,6 +83,11 @@ Approximate number comparison (significant_digits after the decimal point in sci
 Number To String Function
 -------------------------
 
+The default formatter rounds numeric values only. Date, time, datetime,
+timedelta, and NumPy datetime values pass through unchanged, including when
+dictionary-key comparison uses numeric precision or ignores numeric types.
+Numeric precision does not round or merge distinct temporal keys.
+
 number_to_string_func : function, default=None
     In many cases DeepDiff converts numbers to strings in order to compare them. For example when ignore_order=True, when significant digits parameter is defined or when the ignore_numeric_type_changes=True.
     In its simplest form, the number_to_string_func is "{:.Xf}".format(Your Number) where X is the significant digits and the number_format_notation is left as the default of "f" meaning fixed point.
diff --git a/deepdiff/helper.py b/deepdiff/helper.py
index 5143a3b7..90fa2683 100644
--- a/deepdiff/helper.py
+++ b/deepdiff/helper.py
@@ -468,14 +468,17 @@ def get_doc(doc_filename: str) -> str:
 
 def number_to_string(number: Any, significant_digits: int, number_format_notation: Literal['f', 'e'] = 'f') -> Any:
     """
-    Convert numbers to string considering significant digits.
+    Convert numeric values to strings considering significant digits.
+
+    Temporal objects belong to the broader comparison ``numbers`` group, but
+    are not numeric values to round. Preserve them like other non-numeric input.
     """
     try:
         using = number_formatting[number_format_notation]
     except KeyError:
         raise ValueError("number_format_notation got invalid value of {}. The valid values are 'f' and 'e'".format(number_format_notation)) from None
 
-    if not isinstance(number, numbers):  # type: ignore
+    if not isinstance(number, only_numbers):  # type: ignore
         return number
     elif isinstance(number, Decimal):
         with localcontext() as ctx:
diff --git a/tests/test_diff_datetime.py b/tests/test_diff_datetime.py
index c3905291..728c89e7 100644
--- a/tests/test_diff_datetime.py
+++ b/tests/test_diff_datetime.py
@@ -1,5 +1,7 @@
 import pytz
-from datetime import date, datetime, time, timezone
+import pytest
+import numpy as np
+from datetime import date, datetime, time, timedelta, timezone
 from deepdiff import DeepDiff
 
 
@@ -123,3 +125,37 @@ def test_datetime_within_array_with_timezone_diff(self):
         assert not DeepDiff(d1, d2)
         assert not DeepDiff(d1, d2, ignore_order=True)
         assert not DeepDiff(d1, d2, truncate_datetime='second')
+
+
+@pytest.mark.parametrize("key, other_key", [
+    (datetime(2020, 5, 17, 22, 15), datetime(2020, 5, 17, 22, 15, 0, 1)),
+    (datetime(2020, 5, 17, tzinfo=timezone.utc), datetime(2020, 5, 17, microsecond=1, tzinfo=timezone.utc)),
+    (date(2020, 5, 17), date(2020, 5, 18)),
+    (time(22, 15), time(22, 15, microsecond=1)),
+    (timedelta(seconds=1), timedelta(seconds=1, microseconds=1)),
+    (np.datetime64('2020-05-17T22:15:00.000000'), np.datetime64('2020-05-17T22:15:00.000001')),
+])
+@pytest.mark.parametrize("flag", [
+    "ignore_numeric_type_changes", "ignore_string_case", "ignore_string_type_changes",
+])
+@pytest.mark.parametrize("ignore_order", [False, True])
+def test_temporal_dict_keys_preserve_identity_with_numeric_precision(key, other_key, flag, ignore_order):
+    """Key cleaning must not round temporal keys or merge distinct instants."""
+    t1 = {key: 1, other_key: 2}
+    t2 = {key: 1, other_key: 3}
+    if ignore_order:
+        t1, t2 = [t1], [t2]
+    result = DeepDiff(t1, t2, significant_digits=0, view='tree', ignore_order=ignore_order, **{flag: True})
+    assert set(result) == {'values_changed'}
+    changes = list(result['values_changed'])
+    assert len(changes) == 1
+    assert changes[0].t1 == 2
+    assert changes[0].t2 == 3
+    assert changes[0].up.t1 == {key: 1, other_key: 2}
+    assert changes[0].up.t2 == {key: 1, other_key: 3}
+
+
+def test_datetime_key_with_ignored_numeric_value_types():
+    """Reproduce issue 550 through the public comparison API."""
+    key = datetime(2020, 5, 17, 22, 15)
+    assert DeepDiff({key: 10.0}, {key: 10}, ignore_numeric_type_changes=True) == {}
diff --git a/tests/test_helper.py b/tests/test_helper.py
index a42407bd..2f2046bd 100644
--- a/tests/test_helper.py
+++ b/tests/test_helper.py
@@ -304,3 +304,17 @@ def test_add_root_to_paths(self, test_num, value, expected):
     def test_get_semvar_as_integer(self, test_num, value, expected):
         result = get_semvar_as_integer(value)
         assert expected == result, f"test_get_semvar_as_integer #{test_num} failed."
+
+
+@pytest.mark.parametrize("value", [
+    datetime.datetime(2020, 5, 17, microsecond=123456),
+    datetime.date(2020, 5, 17),
+    datetime.time(22, 15, microsecond=123456),
+    datetime.timedelta(seconds=1, microseconds=123456),
+    np.datetime64('2020-05-17T22:15:00.123456'),
+])
+@pytest.mark.parametrize("significant_digits", [0, 3, 55])
+@pytest.mark.parametrize("number_format_notation", ['f', 'e'])
+def test_number_to_string_preserves_temporal_objects(value, significant_digits, number_format_notation):
+    """Non-numeric temporal values pass through the shared formatter unchanged."""
+    assert number_to_string(value, significant_digits, number_format_notation) is value