so if i'm soaking a carboy in it, doesn't help/hurt to soak for a couple days? usually i'll put half a scoop in the carboy, fill it to the brim, and let it sit for a couple days after emptying.. tends to work fine but would it be the same if i just did it in the afternoon then rinsed before bed?
The oxygen action only lasts for the 3-4 hours, but continued soaking will help loosen other debris and aid cleaning.
My procedure is to rinse carboys and buckets thoroughly with water and remove any debris that I can get to with a soft cloth first. Then I soak in Oxiclean for a couple of hours to remove the remaining stuff before rinsing and draining to dry.
I thought that I read 6 hours for the active life of Oxiclean on their website, but whatever, longer than that is a waste. If the krausen hasn't come off by then, you'll have to scrub. (Although it always has done the job for me.)
Anything longer then 24 hours and I've found that it leaves a film that's a PITA to remove. Rinsing is much easier if you do it by the next morning at the longest.