Most manufacturers say 2 hours in the safety guidance but check your brand of car seat. This is also what we were told when we purchased ours by the lady in the shop.
30 minutes I believe until they are older than 12 weeks. But some car seats that have a lie flat function it can be longer - just check with the manufacturer. X
30 minutes for newborn, 2 hours for older children. Even if it's a lie flat car seat the same limit applies.
If your seat has a lie flat option then 2 hours if not it’s no longer than half hour 45 minutes because of development being restricted plus restricted airway from the positioning and being unable to lift own head x
The recommended time limit for a newborn in a car seat is 30 minutes