To prevent too-early germination, it might help to put the jugs in shade or part shade. I use my deck which faces northeast and gets morning sun only. Once they sprout, cut the tape and flip the jug "roof" open so the seedlings get lots of air and avoid frying. That milk jug becomes really a hot greenhouse in hot sun. At night, if temps are cool, flip the top closed. If it gets really cold, like below freezing, I cover them with a blanket .
I've also wintersown toms in cups half filled with potting mix, then placed the cups into a covered bin. When they sprout, I remove the lid from the bin. I add soil to the top so that the plants stem is buried deeper. Even though the plants can seem small to start, they have amazing roots and grow fast once the warm weather comes. This was in April 2012
In August
Karen