About ever two hours
Proof:
The longer the drive between stops, the longer the resting period needs to be. You may prefer, for example, to stop for 10 to 15 minutes
every couple of hours, rather than taking longer breaks less
frequently. You will need to consider your passengers as well,
particularly children and animals.
news.kendallautoalaska.com/classic/Articles/how-often-should-you-stop-on-a-road-trip
