Pulled pork is done when it is done, there is no formula. Some butts are tougher than others for various reasons: genetics of the pig, age, diet etc... and just need more time. Id advise to smoke at a hotter temperature if you are in a hurry, 275-300 if you dont have time for low and slow at 225. Leave it in the smoker the entire time if you can. The butt is done when you can pull the bone out with your fingers from the meat. Thats the best indicator that the connective tissue has dissolved enough and ready for shredding.
Use briquette charcoal, I like Kingsford. Normally I like to use lump charcoal but the irregular shapes will make taming and controlling the fire more of a challenge. Lump also ashes less than briquette; ashes need to be dealt with over the course of long smokes as accumulation will eventually choke airflow. But for your first time, stick with the consistent nature of briquettes for now. Do not get lighter fluid impregnated briquettes, just regular kingsford.
Smoke wood: don't get chips as these burn up too quickly. Get wood chunks. I like to use a combo of mesquite & hickory for the base smoke woods and for pork I like to add apple as well. Smoke is like salt, you can overdo it. I typically add 4-6 fist sized pieces in the first 1.5 hours and then 2-4 after that. You can get away with 2 more pieces after hour 4 but tread carefully for fear of overdoing it.
Fire the smoker first without smoke wood and let it reach operating temperature. The smoke exiting from the vent should be blue/gray. Thick white smoke is acrid and will impart a bitter note to your meat. You typically get white smoke when the smoker is cold. Put your meat on the rack when the smoker gets hot, then open the charcoal area and add your smoke wood.
Your smoker should have airflow vents that control the rate of combustion and therefore temperature. Solid fuel doesnt make instantaneous temperature adjustments like propane. When you open the vent, the extra air allows more fuel to catch fire and you will see your temperature increase 15-30 minutes later. Same goes for decreasing the airflow, parts of the fire have to extinguish when you narrow an air vent. Make incremental adjustments and have patience for the results.
If you must for whatever reason; smoker not maintaining temperatures or you just need to speed it up, you can transfer to the oven at the expense of flavor. Wrap in foil and stick an oven safe thermometer into the meatiest thickest portion of the butt and away from any bones. Maneuver the thermometer where you can read it though the over window. I remove my butts typically at 195-200 and attempt the bone test. If it doesnt pull, it needs more time.
Is this for a party where you will be serving this to guests or for your own consumption? You have 2 simultaneous learning curves here to master: learning the smoker and how to tend a fire enough to stabilize the temp and keep where you want it. And learn how to actually tell the done-ness of pork and know what to look for when cooking. You may want to have a backup plan in case the meat is not done in time.
Your one consolation is that for a first time smoke you picked the best kind of meat: pork butt. Its very forgiving, loaded with so much fat that it almost never will dry out. It can take many mistakes and still make great pulled pork. Try it again after today's attempt when you can plan this one out better. Good luck.