how long to smoke a pork shoulder

I would say get a probe thermometer and stop guessing. Really.

Typically 10-14 hours on a Boston Butt for me, I smoke at 225-250. Are you talking about a true picnic shoulder?

I've tried brining, to be honest I really didnt see the benefit. Mustard slater plus a good paprika based rub and you'll be fine.

What they don't tell you:

The amount of smoke flavor that enters a butt or shoulder decreases dramatically after only 3 hours. It's gets to the point where you would barely notice the flavor difference of a 18 hour smoked shoulder or a 10 hour smoked shoulder.

The internal temp to pull apart the the pork should be around 180.

There is a short cut to get around the 1.25 hour per lb rule if you are short on time. Smoke the pork at 225 for 3-4 hours (the right amount of time to get plenty of smoke flavor) Take the meat of the smoker and wrap in aluminum foil. Turn on your gas grill or bring any grill to a temp of around 500-700 degrees (depending how fast you need it cooked). Then just cook the meat to the proper internal temperature. After is reaches temp, pull off grill and put the meat (still wrapped) in a cooler for 30-60 minutes (no ice). After 30 minutes, separate and enjoy.

Now, most people will be against this. No one would ever do this in competition, but if it's just for family and friends and you're pressed for time, it works amazing.

I have a thread going right now about my first time to cook on my BGE and there is no way in hell I would do this short cut, but I have done it before and most people don't even notice. Any shoulder or butt smoked at home taste way better than any thing you can buy at any BBQ restaurant.

Also, the 30-60 minutes wrapped in aluminum foil and placed in a cooler should be done whether you're doing this short cut or not.

ETA: Of course there is no RIGHT way to smoke anything. It's all a matter of preference, bias opinion, and teachings. I am never against trying anybody else's methods.