The 5 lb butts could take 7.5 hrs as the meat will plateau at around 170* for 2-3 hrs while the fat renders. 90 minutes per pound is not unusual. Your briskett will take roughly 70 minutes per pound, maybe longer.
They're done when their done, but if you think 3.5 hrs is long, you've got a longer wait. Based on your posting time, you may have already figured this out. We often start pork butt and brisket smokes the night before we want to eat.
Have you read Pork Butt 101 and Brisket 101? Read the forum topics on each meat also. Ton of information.