If you are on real-time pricing for your electricity usage, this can save you money. If you are not on the program, it will not apply, as you are paying the average price all day long (and possibly more money, depending on when you use the most electricity.)
To precool your home, simply run the air conditioner in the evening, overnight and during the morning hours when electricity is cheaper. Then increase your thermostat temperature setting or turn off your air conditioner during the afternoon. The goal is for your air conditioner to idle during the highest priced times, especially between 2 p.m. and 5 p.m.