Should I be wearing Invisalign overnight only?

Sounds like a recipe for a poor or delayed result. Think about it. You move them while sleeping, then they drift during the day, then, you move them while sleeping and they drift again the following day.  If this doesn't create problems, at a minimum it will take much longer to move them than if you were to just wear them as close to 24 hours a day as possible.

I have all my patients wearing 24 hours. You might want to ask you orthodontist if your treatment would progress quicker if you wore it for the 24 hour period.

I am not sure why you would be told to just wear Invisalign aligners at night if you want to move your teeth.  Wearing them part time will not likely result in adequate tooth movement.  Invisalign recommends 22 hours per day, and I do too.  You may be able to wear them a little less often than 22 hours a day and have your teeth move, but the less time you wear them throughout the day, the less effective they are.  
I do recommend to my patients to wear retainers at least 8 hours a day in order to maintain where their teeth are currently at.

Dear mhrand66, You must have misunderstood your dentist. To move teeth predictably with Invisalign, the aligners must be worn a minimum of 22 hours per day though I have found that a little cheating is okay.  However if you use them fewer than 20 hours per day, you run the risk of the teeth not properly moving or even possibly damaging the roots and bone. Orthodontics is the simple principle of placing a constant, sustained force on teeth and then letting the bone remodel. Only wearing them at night will move the teeth but by not wearing the aligners during the day, the teeth will spring back because the bone has not had adequate time to remodel. You must have misunderstood your dentist. This is a pretty basic concept.