How about setting about a max daily limit of post that can be accepted. I think putting it between 12 to 15 might be good idea. For me , I have currently off days from jobs as Sunday and Monday so I might be much more active on those days. But setting max post limit for a day will be fair to everybody.
You more than faster from me. I was just writing this post exactly. However this would be best solution. Make maximum post count for per day. Best post count per day would be 13 in my opinions. Because 15 is minimum post count, so in order to continue participate on campaign at least we have to active 2 days. So just set max post count 13 since maximum pay post is 60.
I don't know Hhampuz mentioned to whom, but I always try my best to spread my post over week even though I am not active any signature campaign. Obviously you have reserved right to remove anyone any time and choose best as per your requirements. I know and believe you choose always best candidate. Keep up your good work.