It is more unlikely that anyone would be interested to vote on a post by compromising their curation reward when they can vote for another post that is less than 24 hours and get the full curation reward.

I haven't seen the code but I don't think this is right. If no one votes in the first 24 hours then you still get all of the curation rewards if you're the only one to vote. The only thing that gets cut after 24 hours is the weight, but weights determine the share of curation rewards, not the total.

EDIT: From the additional information added at the bottom of the post I'm now sure this is correct. There is no penalty to voting after 24 hours as long as the post isn't already heavily voted.