Funny you should say this because I actually had the same thought initially and even included it in an earlier draft of this post (yes I go through a few rounds of drafts and revisions for my posts!)

While I agree that would definitely help stop people from avoiding downvotes by voting at the last minute, it could potentially cause other problems.

For example it would allow people to downvote content they don't like without leaving an opportunity for the rest of the community to upvote it back up. I think that is important for the community to be able to combat "bad" downvoting.

Still i'm not really sure if that would be an actual problem or not, and I still like the idea overall of allowing more time for downvotes than upvotes.

I'm interested to hear what others think about this subject!