Ugh, I've had bad experiences with yellow lol.. I have a female now in time out (for good) as she is waaaay too aggressive. Such a pretty innocent looking yellow too.
I wish you luck on the yellows!
I've left pairs in the tank for 1-2 weeks before with no issues.. but generally after a few days with nothing you can pull them and seclude them for a couple days to "rest" them and try again. Virgins sometimes will take a bit longer, sometimes a week or so. Just don't disturb them if possible.. the more they see you and you do things to the tank, the longer it may take.