I set a bounty on a question but no-one's answered. It says I have 23 hours to award a bounty. What happens next?
From the bounty help page:
If you do not award your bounty within 7 days (plus the grace period), the highest voted answer created after the bounty started with a minimum score of 2 will be awarded half the bounty amount (or the full amount, if the answer is also accepted). If two or more eligible answers have the same score (their scores are tied), the oldest answer is chosen. If there's no answer meeting those criteria, no bounty is awarded to anyone.
Basically, nothing happens. You have already given up reputation to set the bounty. Those reputation points simply disappear if there is no one to award the bounty to.
Bounties are more useful on StackExchange sites with lots of users and questions. On ours, I expect that regular users will see all new questions.