Also, keep in mind that in most cases VNAV
won't actually change the altitude for you. You set the altitude on the autopilot on the glareshield and VNAV works to achieve and maintain that altitude. VNAV can tell you when to stop climbing and start descending, but if you are at your TOD and still have altitude set on 36000, you won't be going down anytime soon.
You'd need to actually set the altitude lower before the TOD, then when passing the TOD VNAV will start taking you down towards that altitude etc. VNAV can also be a bit picky, so make sure you get it right when entering in data at the preflight stage.

Alex