Take a bike with you...a bike is invaluable for a visit to the Valley anyway. Get up early, put the bike in the car, drive and park the car in the lot by the tunnel. Give yourself at least a half hour to get back to the lodge on the bike (take gloves and a hat, it's chilly on a bike that early, especially if you're hurrying a bit). You can leave the bike at the Lodge in a bike rack to pick up later. Get the bus tickets the night before.
Should be a nice hike, and the bus ride to Glacier is enjoyable, though I wouldn't count on getting picked up along the route. The loop is also nice, but it puts a more relaxing slant on the hike if you don't have that 4.6 mile uphill hike to start it off (which is a nice hike on its own).