Nole09041 it looks like your going to have a great BBQ on the 4th thanks to Indy and the others giving great advice. As pointed out temp rules over time. Rules of thumb get some into trouble, 1.5 hours for pork butt, that may work great for some but what if someone is cooking at 275º and another is cooking at 225º, or how about the size of the butt or the heat loss of the cooker, etc. 321 and 221 are given as rules of thumb for ribs, but again, we all have different smokers with different inherent capabilities, different ambient conditions, etc. So even the sacred 321 or 221 is only a rule of thumb, and the guide for ribs is tenderness, how the meat comes off the bone.
Yesterday for Father's Day my son cooked on the weber kettle for me, our go to meat for grilling is usually Tri Tip. While he does Tri tip on his gas grill, we were cooking on charcoal briquettes and the timing was different. I almost always cook with timers so I know how long something has been cooking, plus meat thermometer. So my son sticks in the thermometer when he turned the meat, and it said 120º, and commented that we don't have long to cook. However since we also had a timer, I knew from cooking tri tip at least a 100 times over the last 10+ years that 10 minutes on the thickness of that particular meat, the reading was inaccurate. So I encouraged him to check the meat in a couple of other spots. Sure enough the temp showed 100-105º in the other spots. So with a combination of both time and temp plus some experience, you will eventually produce consistently great tasting meat cooked perfectly.
Enjoy your 4th