There's no hard requirements just as long as you make the posts within the 7 day period. However I don't like it when I check someones history and this is what I see:

7 days ago
14 days ago
21 days ago

So they are only making posts just after I've sent payment and then they do nothing more for the rest of the week and it makes it feel like they are bots or something.

No new rules yet, I'm just going to remove people that are inactive or behaving like in the above example, no need to worry for you