As someone who autistically grinded 200+ bounty targets for a leaderboard, it definitely has it's highs and lows. I play Bounty Hunter and choose targets wisely. Usually people with higher bounties are people who have mass amounts of RDMs under their belt, which pump the bounty, or they're mods in sits which makes things awkward because well, you can't get into Sitland.
Many things can ruin your bounty hunt. The target leaving. Them as mentioned, being in Sitland. Or even you dying to someone who RDMs you or you getting caught in the crossfire. There have been countless times where I've accepted a bounty and left via one of the many exits through spawn, and a non-target has killed me. Which then makes me fart around for 180 seconds with my thumb up my ass. And of course, bounty scrambling. All which will put this on cool-down.
I'd personally be all for lowering the cool-down on selecting a new bounty. And to balance this so you're not just picking the same target over and over, is to make cool-downs for individual targets to be hunted. I.e, You just took a hunt on Bob and killed them. Bob has since racked up another bounty. But you can not take a bounty on him after x amount of time.
In general Bounty Hunter feels like a very niche class that is so funny to see when it gets x3 job xp. Because most of the time you won't be able to benefit from increased XP rates with the long cool-down.