There are two factors which have impact on taxes:
1. number of sold players in last 14 weeks
2. how long player is in club.
Factor 1 is updated only once per week, during financial update, it's at night between Sunday and Monday. This factor doesn't change during week and have impact for all players during whole week.
Factor 2 is updated every day and individually for every player. Taxes can change only if number of full weeks increases.