I got asked to smoke a 4 pound boneless pork loin for Sat. How long will it take to cook on smoker at @250 degrees. Thanks

In an oven, 20 minutes per pound at 350 degrees is about right.

May I suggest a meat thermometer. That's the ONLY way to know for sure it's cooked to the proper temp without under cooking (bad) or overcooking and making it dry.

I always brine my whole loin and then put some rub on the outside. Loin is so lean that I like to cook it a little hotter. Low and slow tends to dry it out. I mostly go 275-300 to an internal temp of 160. Mostly only takes 2-3 hours.

Ditto I completely agree!

If you want it to fall apart like pulled pork,I would let it get to around 190 to 200 .

I never cook a pork loin without brining it for 12-24 hours. I think it really makes a difference in the end.