If you look at the bottom left corner of the relay picture, you’ll notice IN1…IN4 - remember which GPIO pins went to which IN1…4 terminals on the relay.
IN1…IN4 then corresponds to K1…K4 on the relay’s power terminals on the right side of the relay counting from top to bottom.
The best way to test is you can use Node Red, and map your GPIO as I displayed to your timer node, and if your power gang box is still open you can actually see LEDs on the relay board light up as you turn them “on” in node red. You could also just hook up a desk lamp to power if the box is closed up and it’ll of course flick on when you activate the node in Node Red.