When travelling with baby I know you need to take a break after 2 hours and get Bub out. How long of a rest should you take before continuing the drive if the trip is longer than 2 hours?

There is no definite time frame in terms of “how long” a baby should be left to sleep on an inclined surface like a car safety device, or how long the break should be.
Most safety organizations like Red Nose, Kidsafe, Raising Children Network suggest 2 hours, as this is the time that drivers should “take a break”
However, there is, concern expressed about baby being left for long periods asleep with chin on chest & the risk of airway being obstructed.
https://rednose.org.au/article/are-there-recommendations-for-car-seat-or-baby-seat-use

Product Safety Australia (ACCC) also provides the following:
https://www.productsafety.gov.au/products/babies-kids/kids-equipment/childrens-car-restraints