Advice Please! Long car journey with 5 month old

[NCAFGS]

We're doing our first long drive soon. I'm aware car seat manufacturers say maximum of two hour chunks with getting out etc in between, so initially we were going to do exactly this and try and sync the drive chunks with her nap time times in the day. Problem is that she now won't sleep for more than 30/45 mins these days bit will link sleep cycles at night and sleep for a solid 8-9 hours.

She has good head /neck control and is half way to sitting up unsupported, I'm sure she'll be doing it in 3-4 weeks maybe?

Our car seat reclines both in and out of the car, not perfectly flat but it reclines a little.

I keep getting told by family /friends they do or have done long car journeys with their babies at night in one long stretch.

Our journey is going to be 4 hours in one go. I'd been sitting next to her so can check on her breathing. I could even get one of those breathing and heart rate monitors.

Night or day WWYD and what have you done?

2 hour rule for car seats is due to babies dropping oxygen saturation overtime due to position, and taking them out for even 5 mins restores it back to normal levels. You will not be able to see saturations dropping by just looking at her. If her head slumps, yes, but saturations drop even when the head is not slumped forward. I would still make a quick pit stop for 5 mins at a 2 hour mark, doesn't have to be anything major, just take her out of the car seat for 5 mins or so.

We did a 4.5 hour car journey with a 9 month old, and he was fed up with the whole affair after the first stop. No amount of toys and entertainment would convince him otherwise. I spent the last hour of that journey frantically singing 'Wheels on a Bus', it's now etched in my memory. So yes, I would travel early early in the morning to get as much sleep time for baby as possible.