Not everyone leaves a light on at first, so however long you have left it on is already more than the minimum. I think the idea is just to leave it on until the worms have gone down. That would probably be a few minutes to an hour. Why don't you turn the lights off now and just check every day to make sure the worms are staying down. If they do try to leave the bin, the problem is something other than not having a light on!
mbetts