Can't Promote Older Posts With The New Promote Post Feature?

I just tested out the new promote post feature on an older post, and it showed up in the Promoted category for less than an hour, then disappeared. Is this the way it's supposed to work? Or only for posts pas the initial payout date?

I also ended up paying 21 SBD instead of the 2 SBD I had intended, because the input field for the amount is horizontally squished to the point of not displaying the amount you enter, on my iPhone, anyway.

Hmm, I think some refinement of this feature is in order.