First... has your main tank been cycled? Not just "setup", but has it gone through the whole ammonia/nitrite/nitrate cycle? It needs to have a population of bacteria built up and the only way to do this is to supply it with an ammonia source to start things off. There used to be a bunch of good member written articles here about acclimation, cycling, etc... but I've lost track of where they went during the recent upgrade. If I can find them, I'll point you towards them.
OK... your other question has a couple issues. A 2-day quarantine is really not going to do anything for you. If you're going to quarantine, a minimum 4 weeks is recommended so that any diseases/parasites will become obvious and "show themselves" so you can treat them before infecting your main tank. Two days isn't long enough for the fish to really show you any symptoms.
In two days, you will start showing some ammonia if you haven't cycled the tank. Do you need to cycle it? No... just be prepared to do daily (or twice daily if need be) 30% water changes to keep the ammonia and nitrite levels down. In the end, it really should've been cycled, but there's not much you can do about it now. Mix up a fair amount of salt water and be ready with the test kits.
Or take the fish back to the LFS
until you're ready.