i have a 5 gal with no gravel, 2 silk plants, and a plastic cave. i tear it down after each use, scrub thoroughly and refill with water from my other tanks to jump-start the cycle. when nothing else is in it, i have an apple snail to keep it going. it stays running all the time, so i can qt new animals i decide i absolutely "need" that i wasnt planning on getting.
time in quarantine depends on the animal and wich shop i buy it at. usually, its 2 weeks to a month, maybe more if its from a bad store.