pip install python-dateutil
>>> from datetime import datetime, timedelta
>>> from dateutil import relativedelta
>>> d1 = datetime.now()
>>> d2 = d1 + timedelta(days=285, hours=14, minutes=32, seconds=19)
>>> r = relativedelta.relativedelta(d2, d1)
>>> r.years, r.months, r.days, r.hours, r.minutes, r.seconds
(0, 9, 10, 14, 32, 19)
>>> from datetime import datetime, timedelta
>>> from dateutil import relativedelta
>>> r = relativedelta.relativedelta(datetime(2019, 12, 25), datetime.now())
>>> f'{r.months} мес {r.days} дн {r.hours:02}:{r.minutes:02}:{r.seconds:02}'
'9 мес 10 дн 04:32:01'