Malachite green is nasty stuff, also quite ineffective against C. irritans
. More often than not it's a miss treatment. Some inverts will tolerate it but there is a good chance you will lose some, corals are not going to like it at all. Depending on the coral species you have, some may not survive it.
Depending on the severity of the infestation, you can easily wait 4 days. I would suggest however you get some sort of seeding material going in the main for bacterial colonization. If you already have a HOB
filter or a few bioballs, they will help immensely.
Once the quarantine tank is set up, fill with water from the main tank, add the biofiltration and get the temp stable. Once accomplished the fish can be transfered quickly. Choose a more appropriate treatment though. If the eel is part of the problem, <<hyposalinity>>
must be used. If the eel is not to be treated, (eels being highly resitant unless a heavily infested tank), you can opt for a copper based treatment instead. Hyposalinity is still the most tolerated of any treatment method and should be the preference. Any treatment chosen though should be performed in a QT