I believe the USPS has worst case requirements of 56 kWh per vehicle per day. That's assuming very low efficiency and very long route. Assuming they have 208V 3-phase 200A service then perhaps they charge at the equivalent of 1 vehicle completely each hour. 10 a night is no problem.
As a practical matter, most routes are not 70 miles, they're more like 25. And the truck probably gets better efficiency than 800 Wh/mi.
Yeah that is a major perk of the new postal trucks both EV and ICE is that they will finally get Air conditioning and an adequate heating system. The LLV had no AC which led to many issues in hot climates, and the heater was not large enough to heat the cabin well with the window open all the time.
As a practical matter, most routes are not 70 miles, they're more like 25. And the truck probably gets better efficiency than 800 Wh/mi.