I want to roast, Matilda, Maple & Garlic Pork Shoulder with Crispy Skin. what adjustments need to be made if I can't cook it for 18 hours ??

I think that might work! I'd keep an eye on it, and after about 3 or 4 hours I would start taking the temp to see where it's at.
Good luck!

I'm thinking I can roast it for 9 hours and I'd put the rub on it the night before , what do you think?

the longer and slower you are able to cook this, the crispier and more falling-apart the pork will be. I would possibly up the initial roasting time at 450*, then roast it at a higher temperature (like 250*F) until it's done. The cooking time will depends on the weight of the shoulder you're roasting. The meat is done when the internal temp registers about 175*F.

The standard measuring time is about 20 minutes per pound at 350*F, with some time after to sit and let the juices collect. But if you're roasting at a lower temp, it will take longer.

My guess- and don't take this one to the books- is that for about 5 pounds of pork, it will probably take about 4 hours.