Can the instantaneous velocity of an object at a given time instant be greater than the average velocity over a time interval that includes the given time instant? Can it be less?

Of course it can be more, and less.

start with a velocity of 10m/s for 4 seconds, then stop for 46 secnds, .

Avg veloity= distance/time= 40m/50sec=0.8m/s

During the first four seconds, inst velocity is greater than avg velocty,in the last 46 seconds it is less than avg velocity.