At this question I was able to award the bounty 25 minutes after it expired. Unfortunately I forgot to screenshot this, there was a message like "This question had a bounty ... that has expired 25 min ago", but the award bounty icon was clickable and so I did successfully. Is this a bug or the answer to the "I missed awarding my bounty in time" problem? The question did not show up under featured questions, so being able to award the bounty within some grace period actually seems sensible.
edit since bounties are now revision events: