Yes add the right amount of stabilizer (in a sock) now
If you won't be backwashing for a few days, you can put the sock in the skimmer basket (you could also turn the sand filter to recirculate overnight so that the CYA doesn't get trapped in the sand and get backwashed out in a few days, in theory)The stabilizer takes a little while to dissolve completely. It is safe to squeeze the sock after it's soaked to aid in disbursement