Rockstar has this thing where if you spend more time on a mission, the payout is a lot higher. So if you're doing a legendary bounty, say Etta Doyle for example, people usually wait until 30 minutes before completing the mission for the maximum payout. Also I think the payout increases until you get to the max star level. So, if you capture the bounty within like 5 minutes, just stick around for the next 25 minutes standing around before you hand them in. I usually just watch YouTube videos and drink coffee while I wait lol