Both peaks and lows are not that predictable or regular. A storm at night will drive prices down because of wind turbines. That can be predicted days in advance

Both peaks and lows are not that predictable or regular. A storm at night will drive prices down because of wind turbines. That can be predicted days in advance but it requires access to weather forecasts. Certain events such a sport games or TV shows could drive the price up. That could be predicted but requires more than a timer. For a heat pump from air the efficiency depends a lot on the outside temperature. So the best time to run it might not be when electricity is cheapest.