It is a rolling schedule. At least, that is my understanding. So for the x per day ones, it will look at how many you have done in the last 24 hour period.
Reset Time
When does the site reset the limit of Tactics, lessons etc??
This one previously said it was reset based on the Chess.com US Pacific time clock.
https://www.chess.com/forum/view/help-support/limited-tacticstrainer-question
When does the site reset the limit of Tactics, lessons etc??