Используйте встроенный модуль Datetime из Python и пример ниже:
>>> from datetime import datetime
>>>
>>> # read
>>> d1 = datetime(2020,7,9,15,48,26,603)
>>> d2 = datetime(2020,7,9,15,58,26,648)
>>>
>>> # calculate difference and print total amount of seconds
>>> diff = d2 - d1
>>> print(diff.total_seconds())
600.000045
>>>
>>> # keep the difference as a timedelta object
>>> diff
datetime.timedelta(0, 600, 45)
>>>
>>> # you can check the calculation
>>> d1 + diff == d2
True