Some datetime related tests fail at night

My feeling is these failures only happen arround the change of days.

FAILED tests/app/v1/routers/test_materials.py::test_materials_aggregations[date-histogram-interval] - AssertionError
FAILED tests/app/v1/routers/test_materials.py::test_materials_aggregations[date-histogram-metrics] - AssertionError

Anyhow, they definitely happen occasionally.