Any time before the afternoon should be fine and the driving time is 1.5 hours. I’ve done it in 1.25 but that’s at about 80 the whole way.

You should certainly leave before 3pm on Friday. Friday traffic starts very early down route 3 between Boston and the Cape. Better to leave early or wait until after 7:30pm than to leave during a Friday rush hour.

Yeah, an hour and a half is about right. Since it’s not summer any more, traffic is a little less worrisome. Depending on where you are in Boston, you may have to deal with some regular rush hour traffic leaving Boston until at least 10pm. Unfortunately, rush hour starts really early (sometimes as early as 5:30pm) in Boston. If you do decide to go during rush hour, you might be stuck in traffic for somewhere between 20 minutes and an hour, depending on what roads you take and if there are unforseen circumstances like accidents. If you leave at 10, though, it should give you plenty of time for a nice day trip.

The only other place you might encounter traffic is right before you cross the Sagamore bridge, which takes you onto the Cape. That delay shouldn’t be more than a few minutes, though.