Then you're simply making it a pay-to-use website, which is probably not the best for the community. 4 hours and 5 posts is not a huge amount, it really shouldn't take you that long if you actually plan to be active in the future.
I don't think it would make it pay-to-use website since:
1) deposited money could be returned back after the person actually spends 4 hours and submits 5 meaningful posts (if he/she is not a troll).
2) it could be just an option for those who don't want to spend 4 hours for posting 5 meaningless posts
