You’re mixed up.

Time is not a variable in the power equation. If you want 400 kilowatts, you can get it in one microsecond if you want. Or, you can drag it out over 10 minutes, ten hours or 1,000 hours, doesn’t matter.

Ohm’s law tells us that P=IE, or “Power equals Current times Voltage”, so if you take a source producing a pressure of 4,000 volts and have a low enough resistance load (including the wires) to pull 100 amps out of it, you’ve got your 400 kilowatts instantly, and you’ll have it until you shut off the switch.

I think the unit of measurement you were looking for was “kilowatt hours”. Similar name, but completely different animal.