From 5dceb687c0b4dac1e2a8e2ba5b0ef7331044a3ce Mon Sep 17 00:00:00 2001
From: Tyler Sutterley <tsutterl@uw.edu>
Date: Fri, 17 Jul 2026 18:07:05 -0700
Subject: [PATCH 1/2] feat: add function to convert times to `numpy.datetime64`

---
 doc/source/api_reference/time.rst |  4 ++
 gravity_toolkit/time.py           | 71 ++++++++++++++++++++++++++++++-
 2 files changed, 74 insertions(+), 1 deletion(-)

diff --git a/doc/source/api_reference/time.rst b/doc/source/api_reference/time.rst
index 2633419..adfd8ac 100644
--- a/doc/source/api_reference/time.rst
+++ b/doc/source/api_reference/time.rst
@@ -57,6 +57,10 @@ General Methods
 
 .. autofunction:: gravity_toolkit.time.datetime_to_list
 
+.. autofunction:: gravity_toolkit.time.to_datetime
+
+.. autofunction:: gravity_toolkit.time.to_string
+
 .. autofunction:: gravity_toolkit.time.parse_grace_file
 
 .. autofunction:: gravity_toolkit.time.parse_gfc_file
diff --git a/gravity_toolkit/time.py b/gravity_toolkit/time.py
index 09e56ac..b9b0c39 100644
--- a/gravity_toolkit/time.py
+++ b/gravity_toolkit/time.py
@@ -1,7 +1,7 @@
 #!/usr/bin/env python
 """
 time.py
-Written by Tyler Sutterley (06/2024)
+Written by Tyler Sutterley (07/2026)
 Contributions by Hugo Lecomte
 
 Utilities for calculating time operations
@@ -13,6 +13,7 @@
         https://dateutil.readthedocs.io/en/stable/
 
 UPDATE HISTORY:
+    Updated 07/2026: added function to convert times to numpy datetimes
     Updated 06/2024: remove timescale class and leap second calculations
     Updated 06/2023: add timescale class for converting between time scales
         add functions for retrieving leap seconds from NIST or IERF servers
@@ -203,6 +204,74 @@ def datetime_to_list(date):
     ]
 
 
+def to_datetime(timedelta: np.ndarray, attributes: str, unit: str = 's'):
+    """
+    Convert an array into ``numpy.datetime64`` objects
+
+    Parameters
+    ----------
+    timedelta: np.ndarray
+        array of time deltas
+    attributes: str
+        compatible time attributes for
+        :py:func:`parse_date_string <gravity_toolkit.time.parse_date_string>`
+    unit: str, default 's'
+        datetime unit for output datetime array
+
+    Returns
+    -------
+    dtime: np.ndarray
+        ``numpy.datetime64`` array
+    """
+    # verify that units are numpy datetime compatible
+    assert unit in ['D', 'h', 'm', 's', 'ms', 'us', 'ns']
+    # get the epoch and units from the attributes
+    epoch, to_secs = parse_date_string(attributes)
+    # convert epoch to datetime variable
+    epoch = np.datetime64(datetime.datetime(*epoch))
+    # calculate the delta time in seconds
+    delta_time = np.atleast_1d(timedelta * to_secs).astype(np.int64)
+    # return the datetime array
+    return np.array(epoch + delta_time.astype(f'timedelta64[{unit}]'))
+
+
+def to_string(
+    timedelta: np.ndarray,
+    attributes: str,
+    unit: str = 'D',
+    strftime: str | None = None,
+):
+    """
+    Convert an array into string representations of dates
+
+    Parameters
+    ----------
+    timedelta: np.ndarray
+        array of time deltas
+    attributes: str
+        compatible time attributes for
+        :py:func:`parse_date_string <gravity_toolkit.time.parse_date_string>`
+    unit: str, default 'D'
+        datetime unit for output string array
+    strftime: str, default None
+        alternative formatting string for output string array
+
+    Returns
+    -------
+    timestring: str
+        string representations of dates
+    """
+    # convert to datetime objects
+    dtime = to_datetime(timedelta, attributes, unit=unit)
+    # return the string representations of the datetime objects
+    if strftime is not None:
+        # convert to datetime objects and use strftime formatting
+        dtime = dtime.astype(datetime.datetime)
+        return np.array([d.strftime(strftime) for d in dtime])
+    else:
+        return np.datetime_as_string(dtime, unit=unit)
+
+
 # PURPOSE: extract parameters from filename
 def parse_grace_file(granule):
     """

From 464af9f5293aed34ee27fb569598fb261a908b06 Mon Sep 17 00:00:00 2001
From: Tyler Sutterley <tsutterl@uw.edu>
Date: Fri, 17 Jul 2026 18:12:05 -0700
Subject: [PATCH 2/2] fix: use seconds as default

---
 gravity_toolkit/time.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gravity_toolkit/time.py b/gravity_toolkit/time.py
index b9b0c39..8b89c9f 100644
--- a/gravity_toolkit/time.py
+++ b/gravity_toolkit/time.py
@@ -238,7 +238,7 @@ def to_datetime(timedelta: np.ndarray, attributes: str, unit: str = 's'):
 def to_string(
     timedelta: np.ndarray,
     attributes: str,
-    unit: str = 'D',
+    unit: str = 's',
     strftime: str | None = None,
 ):
     """
@@ -251,7 +251,7 @@ def to_string(
     attributes: str
         compatible time attributes for
         :py:func:`parse_date_string <gravity_toolkit.time.parse_date_string>`
-    unit: str, default 'D'
+    unit: str, default 's'
         datetime unit for output string array
     strftime: str, default None
         alternative formatting string for output string array