Most bounty hunters immediately dump the coins they get since they treat it as payment for work that they've done.
As for me, I wait for a few days and see how active the team is after the ICO ends. If the team achieves what they have stated in their road map, I HODL for a long time.
But if delays happen, most of the time I dump them immediately.
If you closely follow the project during the bounty campaign, then long before its end it is clear whether to hold tokens for a long time. However, I prefer to go to the end and wait for the project to be fully realized. I do not sell tokens that I receive from bounty campaigns.