Originally Posted by
szto You can thank a person as much as you want, but you can only rep the same person after giving out rep to 5 others.
This is the relevant part in Dai's post:
What I don't get from your post is that according to your description, you thank people for downloads, and then you aren't able to rep others in the fanfic section. The two things shouldn't affect each other that way. Thanks are endless, but reps per day are limited to a maximum of 10. If there's a user you can't rep, even though you haven't repped them before, you should contact a staff member.
To answer your question though, there's no "count down" for when you can rep the same person again. So if you don't keep score with the reps you give, you'll just have to try till you can rep the same person again ^^;