How many of what fish in what size temporary tank?
Kind of hard to get a good answer to that.. I would think as long as you do enough water changes to keep the water quality right I would say a decent amount of time. Almost similar to the amount of time one would QT their fish. It would help a lot to run a HOB filter and clean it out often to help get uneaten foot and what not out.
I think you'll be ok. A hob filter or similar would help but how long will they be in the temp tank for. Water changes will be helpful either way
I run my qt in this way. Tank water, water changes every other day, but only a 10g so isn't too difficult a process really. I would use ammolock or similar product too