24 hour period is definitely better for posts. With the 12 hour one you had to think what is the right time to post based on your location and time zone as posting it at the wrong time could've made it even harder to be noticed. I'm not sure about comments though, if they also have changed the time period to 24 hours.

You cannot vote for a post a month older because that is the second pay period, after that there are no more payouts for it and no point in voting, so it gets disabled.