As I've mentioned in comments in other places, in-so-far as the rewards curve goes, I think it should be linear from start to finish: the same investment weighted upvote reward from the time something is published to the time it pays out (and 50%-50%, like now, of course). I don't see any reason why we should game each other.

. . . sometimes we see something days later that we'd like to reward the same as if we had seen it in the first 5 minutes.

That having been said, if we need to "gamify", I would strongly argue for 24 hours. Let me explain.

If someone in Australia gets up in the morning and publishes, everyone in Europe would by "punished" by a two hour cap. And that's to say nothing about the person living in the Western Hemisphere! And more so if we have some sort of regression built into the remaining time that accelerates into payout. The same for something posted in the morning in Europe: everyone in the U.S. is penalized! Oh, and Australia too. The same applies to anything done in the U.S.: anybody further west than 2 time zones is punished! Therefore, if we have to do this type of "incentivizing", then I'd think we'd be obligated, out of basic fairness, to give the initial period at least 24 hours, in order to resolve that aforementioned issue.

And, I'd also suggest that there's no point in changing the absolute value of the upvote after that 24 hour period either.

Again, even then, why not just make it linear throughout?

But I digress.

Hope this is helpful, Happy New Year, and, as always, thanks for everything!