how do I set the lights for auto-off?

"Automatic light off system
●
When the headlights come on: The headlights and tail lights turn off 30 seconds after a door is opened and closed if the power switch is turned to ACCESSORY mode or turned off. (The lights turn off immediately if [lock] on the key is pressed after all the doors are locked.)
●
When only the tail lights come on: The tail lights turn off automatically if the power switch is turned to ACCESSORY mode or turned off and the driver’s door is opened.
To turn the lights on again, turn the power switch to ON mode, or turn the light switch off once and then back to [headlights on) or [marker lights on]"
.
https://www.toyota.com/t3Portal/document/om-s/OM47B39U/pdf/OM47B39U.pdf page 245

I park in a garage so I do not want the headlights to stay on for 30 seconds. (if I parked on a long driveway I might want them on for 90 seconds) Only you can decide the amount of light you need for safety.

Page 757 hints that a Dealer or a OBDII programmer may be needed to change the delay on your Prius, unless you have Entune.

Time elapsed before the headlights turn off default 30 seconds, programmable to 0, 60, or 90 seconds.

 

By your left knee there is a button for the auto-off feature. Turn that on. After that all you have to do is turn the headlights to auto or on and leave it like it is. If you want auto-high beams, click the stalk forward and leave it there.

When you turn off the car, and walk away, it should take 30 seconds to turn off.

 

I believe on the Gen 4 Prius 2 the headlights stay on for 30 seconds by default and then turn off as stated above.
I never waited to test mine. I changed the setting so they so they turn off right away.

If you mean auto-high beams, therr is a switch on the lower left side of the dashboard.