I don't have a weekly timetable as I'm not doing Natural Sciences but I know a few Nat Sci students - they do seem to have busier than average timetables, with up to 26 hours of contact time some weeks. Your timetable will depend on which modules you choose to do. Seeing as Chemistry'll be one of your majors, you'll probably have labs 2-6 most Tuesdays and Thursdays, and you'll probably have early starts.
I'm a biology/geology NatSci and yep the timetable is pretty packed. I can't access the chem/maths timetables but I have friends doing them, and I think the workload is similar for all of the majors. Though you may end up with a lot of chemistry labs.
A basic week for me is labs (5hrs), tutorials (2hrs) and lectures (lots!).