Understanding power of a time interval:
Instantaneous power (demand)
The instantaneous power (or instantaneous demand, or instantaneous load) is the quantity of power that something is using (or generating) at any one moment in time. Instantaneous power is measured in kW (kilowatts).
ex: Put your laptop on standby and its instantaneous power will drop immediately. Bring it back to life and its instantaneous power will rise immediately.
If, at any particular moment, everything in your home is switched on, your home might be using 20 kW of power. That's 20 kW of instantaneous power. If, at any particular moment, everything in your home is switched off, your home should be using 0 kW of power. That's 0 kW of instantaneous power.
The instantaneous power of most homes varies constantly.