SECOND FILTER.
I've had this curse for several years now; the transformation is triggered at night. Not every night - no, that'd be too easy - just many nights. Most nights. Sara Lance allows me to stay in the Star Labs, which I've been doing, but frankly I'm tired of wearing my sexy jammies in front of random scientists that happen to be working late. And not eating someone would be a bonus.
And for your first question - minimal, minimal control. I've been told it's possible, but I've yet to manage it. The same person who said it managed to make me transform during the day, but that was mostly because they were threatening my general.