PG&E has a special rate schedule for owners of electric vehicles - E9. If you are using this schedule, there are 2 to 3 periods during the day where the rate changes. The cheapest rate is typically from Midnight to 6am. The schedule is a bit messy, likely due to a bug in the billing software with daylights savings time. They do document the timing, but it ends up making it more complex than it should be. Anyway, I built this visual spreadsheet to cover 2013 and 2014 timings in an easy to see format. The E9 tariff is experimental, and is planned to go away at the end of 2014.