I happened to notice that I couldn’t change/undo a reaction I gave a post a few hours ago. According to a Discourse Meta topic, this is an admin-configurable setting. We have it at 10 minutes right now.
I can see a case where a post gets edited and that changes how someone feels about it and they decide to give it a different reaction (or none at all). It appears that editing the post does not reset that timer.
Jeff Atwood says the intent is to keep users from harassing others by liking and unliking forever, but that feels like a thing we can deal with individually if it happens. I propose we set it to 40320 (28 days). We could make it bigger, but I think we’d catch most cases in that window.