We'll have it cleared up by tomorrow

And this is the manager of the fish department???
At least a month in quarantine is the minimum. Complete quarantine- no sharing of tools, equipment, or transferring anything between tanks. Wash hands between handling tanks.
For extra precaution after the first month add an 'expendable' fish from your tanks to the quarantine tank and watch both fish for another month. The fish from the store might have brought something home that he is resistant to, and not showing signs, but also, your fish might not show symptoms but be carriers of something the new fish is not resistant to. (Is that confusing?)