I think bounty campaign give out their prices base on on the campaign lay down procedures of all bounty payments. Every campaign has a planned budget and stipulated  time of bounty payment time tables. Most campaign will like to pay the price after 30days of the end of the ICO while, some will pay bounty payments 15days after their ICO. There are also situations  where bounty price are being payed in batches ,and at such, the timing might vary .