I'm running an irrigation pump on 240V circuit I added to my breaker panel, and it's working fine with just a switch between them. After my first attempt to add the timer between the switch and the panel failed (kept tripping the breaker when I turned the timer to "on"), I'm hoping to get some direction here. I have the wiring diagram attached. It appears to indicate the 2 wires from the breaker go to screws 2 and 4, while there's a jumper between 3 and what I'll call 0, the un-numbered screw. Then 0 and 1 run down the line to the 2-pole shut-off switch by the pond. Am I understanding correctly?
You have it backwards
While I can't explain the breaker trips in your setup, the documentation for your timer has the line in going to 0 (with the jumper to 3) and 1, with the load (the wires to the shutoff) connected to 2 and 4. The way you have it wired won't work anyway, as the motor would be powered through the timer contacts, which would cause the timer to not time 99% of the time.