It seems insane to me to market this as "the food costs extra at certain times of day" rather than "Happy Hour-- 20% off!"
Happy hours are designed to increase demand.
Surge pricing is designed to capture some of the value that high demand loses to limited supply.
I agree with your framing, but 20 hours of happy hour is a tough sell for PR, but worth getting right.
I also disagree with everyone here saying people will just go to an alternative restaurant, when the entire point is that all the drive thru’s are already full during these periods.