Luckily, you only have a 3+ hour drive. I say luckily because where I am, the drive from my house to the city where our family is located is over 6 hours even though it is still in the same state. Yikes! We've done it a couple of times. Like PP's say, leaving around or just after naptime works, plus a lot of stops. It does help for one of us to sit back there with her. Last, but not least, both our cars have a DVD player in them, and that has been a big plus (but would not have worked at 9.5 months). I would be worried to do the drive at night, because one time we flew with DD at 9 months on a night flight and she slept for about 4 hours, so when we arrived at our destination at midnight, she was wide awake and thought it was morning. But, if your LO is easy to transition from one place to another while asleep, you might do OK. My biggest bit of advice would be to not focus on the clock. Expect trips with little ones involved to take longer than average, and most importantly, make sure DH or DP gets this as well.
