I'm a member, not a board official, but to move your process along a little bit:
You can now bid every 2 hours, rather than the 24 hours.
I think all Priceline meant was that you could submit a bid for the same zone(s) and star level as you had done 4 hours ago. You could raise the bid amount, lower it, or leave it the same. Sometimes hotels have given new room inventory to Price.line so even a bid at the same or a lower amount could make sense.
Philadelphia has lots of zones at lots of different star levels, so even with "little flexibility" there probably are bidding patterns that would let you make quite a few bids just in one session. And therefore explore a range of rates all at once.
If you post back with your dates, desired zones and star level, plus some indication of your maximum budget, I'm sure you will be given a bidding pattern that will let you do the job effectively. The reason for the budget number is so you aren't provided with a pattern that is higher than you'd like to try.
If you aren't yet familiar with free rebid zones, it would be good to study up on those here: Priceline Re-Bidding Explained
Romelle