Just now, when you need to pay depends on when the current balance was on there.
Were the current charges on there when your last statement cut? If so, PIF ASAP so that you meet the 'due date' deadline for your payment that's due right now and are starting with a clean slate.
Once you're paid down to 0, either hold off on using the card until after your next statement cuts (which is when most - though not all, and Orchard may be one of the oddies - cc's report to the CRAs) before using it, or else charge something and PIF as soon as it posts to your account for a few more days, but then do stop using it about a week before your statement date to ensure that everything's posted and been PIFed.
Once that 0 balance is reported (and you should then have 0 min. pmt. due as well, at that point), you can start using the card more normally, but your target for PIFing if you want to keep a 0 balance reporting is that statement date - PIF a week or so before it and try to avoid using the card until after the statement cuts.
If you need the card to report a small balance at some point for score maxing, then follow first steps above to get that first 0 balance reported, use as normal but pay down below 9% before the statement date, let that 9% report, then PIF the remainder immediately afterward to avoid paying interest or accidentally missing your payment due date.
However, with only 2 cards to work with, you might want to check via a post over on Understanding FICO Scoring on whether or not it's best to have both reporting 0 consistently, or one 0 and the other <9% for max scores.
Hope this helps.
