We're going out of town this weekend, and our drive will be about 3.5-4.5 hours each way depending on traffic. DD is 8 weeks old and usually sleeps well in the car, but I would expect her to be awake for part of the drive and be hungry at some point. We'll be driving in the middle of the day.

How long can I let DD stay in the car seat before taking her out? I thought I heard something once about taking them out every 90 minutes or so. How do you handle the length of time your LO spends in the car seat?