Just checking, Is it OK to plug in for less than three hours?

yes. you can plug in for as short a period as you like with no detrimental effects. and welcome to priuschat! what is this 'other non-hybrid' you speak of?

 

pleasure...

 

What's important is that you plug it in. Do it often to increase your EV ratio.

 

I charge the car up after a few miles all the time. I never know when I'm going to need it for some longer running around periods.

 

I was advised by the dealer to set the charger timer for three hours, so it now charges from 1 am to 4 am. It's not a major nuisance to reset the timer every time I have a chance to plug in during the day, but it is a nuisance. Know of any settings that make it easier?

 

Not really.
Also, those are two separate timers, not a single timer with a start time and stop time.

 

As mentioned, Start and Finish are two different timers.

I set Finish at 7:00 AM and Start at 3:00 PM. This way, I know my PiP will be fully charged in the morning and after work.