Don’t hold me to this, but I think Kettleman City is on a 2,500 kVA grid connection (plus solar and batteries). There won’t be any additional throughput unless they increase the grid connection along with the V3 upgrade.
If you are going on the assumption that everyone arrives at the same time with an empty battery, and they are all the same size pack.
There is just no way that all 40 cars charging would be asking for the peak 250kW charge rate at the same time unless someone went to a lot of trouble to arrange the event.