Go to Home Depot. They have some nice timers in the outdoor lighting section. I use a timer set at about 3 hours in the morning. I don't think that the block heater is quite 1500 watts. I think your only looking at about 1000 watts unless the 7.3 heater is bigger than a 6.0 heater. There is no way the circuit breaker that I have mine plugged into would handle anything close to 1500 watts.
When I start the truck in the morning the coolant temp is anywhere from 96 to 103 degrees depending on the ambient temp. Instant heat is a nice feature, but with electric at over $0.18/kilowatt hour I can't afford to plug it in all night long. The $20 timer will almost pay for itself in the first month. I figure it cost me about $10-$12 per month right now to plug the truck in with the timer. It would cost more than that in fuel for warm-up idle time.