For years we’ve been told that exercise improves sleep… But we can’t work out TOO close to bedtime because our core temperature needs to drop for sleep hormones to kick in. So how late in the day can we exercise and still get the sleep benefits? Dr. Kelly Glazer Baron is a neurology professor at Northwestern University… and she says, about 3 hours before bed should be your exercise cutoff time. Within 3 months, you should be sleeping about 45 minutes longer, and getting better quality sleep. Because that’s how long it takes for the improvements in mood from exercise to have a lasting effect on sleep.