diff --git a/.github/workflows/pytest.yml b/.github/workflows/pytest.yml
index 402bbaf..ecb4de8 100755
--- a/.github/workflows/pytest.yml
+++ b/.github/workflows/pytest.yml
@@ -19,27 +19,36 @@ jobs:
         # Test coveralls (with numba disabled) and normal pytest
         test: [ 'coveralls', 'pytest', ]
         # Only do coveralls once; pytest on all python versions
-        python-version: [3.8, 3.9, "3.10"]
+        python-version: [3.9, "3.10", "3.11", "3.12"]
         exclude:
-          - python-version: 3.8
+          - python-version: 3.10
             test: coveralls
-          - python-version: 3.9
+          - python-version: 3.11
+            test: coveralls
+          - python-version: 3.12
             test: coveralls
     steps:
       - name: Setup python
-        uses: actions/setup-python@v4
+        uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}
       - name: Checkout repo
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
+        with:
+          submodules: 'recursive'
       - name: Install requirements for tests
         run: |
+          pip install --upgrade pip
+          # Require setuptools for python3.12 as well
+          pip install setuptools
           # Requirements for running the notebooks as a pytest
           pip install cython ipython
+          pip install jinja2==3.0.3
           pip install nbconvert nbmake pytest-xdist pytest coverage coveralls pytest-cov pytest-notebook ipython_genutils
           # Several optional packages that are imported in the notebooks
           pip install git+https://github.com/XENON1T/laidbax
-          python setup.py develop
+          pip install -e .
+          pip install seaborn matplotlib
       - name: Test package
         if: matrix.test == 'pytest'
         run:
diff --git a/tests/test_halo.py b/tests/test_halo.py
index bee71a5..782e1f8 100644
--- a/tests/test_halo.py
+++ b/tests/test_halo.py
@@ -1,7 +1,7 @@
 from datetime import datetime
 
 import pandas as pd
-from wimprates import j2000, StandardHaloModel, j2000_from_ymd
+from wimprates import j2000, StandardHaloModel, j2000_from_ymd, j2000_to_datetime
 import numericalunits as nu
 import numpy as np
 
@@ -21,6 +21,11 @@ def test_j2000_datetime():
     assert j2000(date) == 3318.25
 
 
+def test_datetime_j2000():
+    date = 3318.25
+    assert j2000_to_datetime(date) == datetime(year=2009, month=1, day=31, hour=18)
+
+
 def test_j2000_ns_int():
     date = datetime(year=2009, month=1, day=31, hour=18)
     value = pd.to_datetime(date).value
diff --git a/wimprates/halo.py b/wimprates/halo.py
index 4f943da..6be8351 100644
--- a/wimprates/halo.py
+++ b/wimprates/halo.py
@@ -67,6 +67,17 @@ def j2000_from_ymd(year, month, day_of_month):
             + np.floor(30.61 * (m + 1))
             + day_of_month - 730563.5)
 
+@export
+def j2000_to_datetime(j2000_date):
+    """
+    Returns date in np.datetime64 instance from the fractional number of days since J2000.0 epoch.
+    It is effectively the inverse of the j2000 function.
+    """
+    zero_value = pd.to_datetime("2000-01-01T12:00").value
+
+    nanoseconds_per_day = nu.day / nu.ns
+    _date = pd.to_datetime(j2000_date * nanoseconds_per_day).value
+    return pd.to_datetime(_date + zero_value).round("s")
 
 @export
 def earth_velocity(t, v_0 = None):