Well, use a little physics and figure out what you're working with. P=IV. That's power (in watts) = current (in amps) x voltage. Assuming a 120v house power point, 600=I x 120, I solves for 5, or 5 amps in your circuit.

So if your power supply is 120v, then you'll be pulling 5 amps (or 2.5 if a 240v system). A 14 amp timer would work just fine.