All purchases are one-time fees. You won't be rebilled.
There is no time limit to pass your evaluation. Just keep our inactivity rules in mind.
Inactivity Rule - Evaluation
Place at least one trade every 20 days. Your account will be deactivated 20 days after your last trade.
Inactivity Rule - Funded
To keep your funded account active, you must place at least one trade per week (Monday through Friday). This is per account, not per user.