I don't see why you would load something that is not going to be used until 20 hours later. That would be a whole heck of a lot of stuff.
Loading every model and texture for every single level at the same time is excessive and you'd be asking for trouble. Running collision response for every single object from beginning to end could also really bog down the machine. Same with physics.
Why not load a model within a few minutes of it's first appearance? Now it's not a burden on the system until it's ready to be used.
Loading a model and its textures will not likely cause anything more than a slight hick-up if you've been cleaning up everything that is no longer being used.