As a homeowner in PG&E territory, you pay different rates for electricity based on the time of day. All homes are now defaulted to what are called Time-of-Use rates for their electricity use. This means power costs more during the hours of 4-9pm daily, which are the "peak hours" when more power is being used than any other part of the day. Avoiding power use during peak hours will save you money. 

PG&E: RESIDENTIAL PRICING INFOGRAPH https://www.pge.com/assets/pge/docs/account/rate-plans/residential-electric-rate-plan-pricing.pdf