I’ve done it in 2 gallons a while back a few times and it’s a good size. I have a diary of one of em.
IF you can, and run that light for the first 3 weeks or so at 18/6 anyhow. There won’t be enough ethylene production in the first month to start flower anyhow.
But if you’re doing this cuz you can’t run another light cycle I get that too.