Right now, peak prices are during peak demand, which is typically in the afternoon. However, there are two factors that may change this over the next decade.
In many places, solar power will soon be a significant portion of the power supply, and solar production matches peak demand. Solar is a sunk cost, so any dynamic pricing is based on being able to scale back production at gas-fired plants and the like. Hence, it may be that power costs will be higher when it's dark, even if demand is lower. Expect peak prices in the evening and morning hours.
Also, as electric cars become a significant portion of the vehicles, demand for charging at night will go up significantly, so peak demand may well be at night. Utilities will certainly work to get car owners to install smart chargers that optimize charging based on power availability with the goal of a full charge by a certain time (such as when you typically leave in the morning). [And of course, by "full," that means 80% to maximize the life of the battery unless you're planning a trip.]
Of course, the combination of widespread adoption of both solar power and electric cars suggests that the optimal time to charge is during the day, but good luck getting that to work for the majority of workers.