At that hour I'm usually sleeping in my bed = I am usually asleep in my bed.
At that time I'm usually driving = I'm usually in my car.
Every morning when the alarm goes off I'm usually in the middle of a really nice dream = I'm usually dreaming.
When he gets home I'm usually nodding off on the sofa.
We often use present/past/future continuous when describing actions in progress at a particular time, be it past, present (now/routine) or future.
It's an entirely different meaning if you say "When he gets home I usually sit on the sofa and nod off" it would suggest that he's so boring he makes me fall asleep.