Isn’t the “vote too old to be changed” a little too eager?
I was reading this question on SO, and wanted to vote up one of the answers, so I did. After researching the topic some more, I found out the answer I upvoted was actually incorrect and the one I voted for wasn't, so I wanted to change my upvote to the other answer. However, even after this short time (under 2 minutes) the system both wouldn't let me remove my upvote, or add an upvote to the correct answer.
I've seen some other questions on this topic, but they all seem to be about changing votes after a longer period of time.