I've got the same deadline - June 28, so I was under the impression that I'd lose some points just because I take only Hilton and my last redemption was less then 3 months ago (March 28).
Didn't happen - I was able to redeem today
So I'd advice anyone who wants Hilton try to redeem a few times until 28 th - their time limit is probably 90 or even 89 days.