How to calculate absolute prepositions

[Ari24-cb24]

10 days and hours after 3 months before christmas 2020

This means:

Take christmas 2020 (datetime(year=2020, month=12, day=25))
subtract 3 months (datetime(year=2020, month=9, day=25)) (if the day is the 31th of the month but the month only has 30 days, go to day 30)
Add 10 days and 2 hours (datetime(year=2020, month=10, day=5, hour=2))

Another Example

3 months before the fifth week of august 2020

This means:

Take the first day of the fifth week of august 2020 (datetime(year=2020, month=8, day=31))
subtract 3 months (datetime(year=2020, month=5, day=31)) (same principle with the days as above)