I voted down an answer and later (after 3 hours) came back to StackOverflow to find a comment which explained that I was wrong and answer was actually correct. However, the system doesn't let me revoke my downvote, because the answer wasn't edited. What should I do? Or more importantly, what would you propose to avoid such situations in future (advising to think more before downvoting doesn't count as everyone makes mistakes).
If you have 2k reputation, edit it yourself.
If you don't, post a comment asking the OP to edit it, and maybe to reply to your comment so you don't forget.
This protection is against the systematic temporary downvote of all competing answers so that yours is at the top of the list; increasing the limit to hours as you propose would defeat the purpose for which the vote lockdown was implemented.
I understand that it's frustrating to honest users, but unfortunately some people decided to abuse the system so now we must all pay the consequences.
I would prefer to revoke a downvoting even years after downvoting. Everybody should be able to change his mind. To prevent fraud, the penalty for downvoting could be preserved.