I’ve had jobs where you get a run sheet with breaks planned in, I never really took a great deal of notice. The way I look at it, so long as you have the truck where is needs to be at the right times, it doesn’t make a jot of difference to the office when you are taking a break so just have it when you want.
The only exception would be if you are carrying high value goods, in which case they might want you to stop in designated places and/or when empty which is fair enough.