Dunno about the VNC, but schools teach one hour preparation, because you can be given just one hour to prepare on the test day. I'd rather my school teach me to plan in 1 hour and get the route a few hours before than the other way around
Edit: Just saw your second post, technically the ATO can give the route to you at any time, however he must give at least one hour. Whether they give you one hour or more is entirely up to them