Just keep them in there until they start ignoring or getting hostile toward them.
Our LFS kept accidentally breeding them because they had the red devils/midas for too long, and they would leave them in there for weeks with all the other red devils/midas and every time I came back they had more and more tanks of them...right now they have 4 40 gallons of their growouts and then the big ones and they are buy 1 get one free.
If you mess up the first time chances are they will breed again...they said they had new red devils about every 3 weeks.