If you sleep too long, you get all screwed up. If I am running on fumes, a half hour is perfect. Usually I spend the whole lunch hour trying to sleep, and only actually sleep for 30 minutes. Even 15 min is surprisingly effective if it is uninterrupted. Once I go past an hour though, I wake up super groggy and out of it. The worst is when you get home at 5:30 and fall asleep until 7:30 or 8:00. You wake up feeling so refreshed, just in time for bed. Face palm.