Yep, happy hours are already well-understood and accepted. As long as they make their hours clear and obvious and standard across their restaurant line.
Shifting to ridesharing's surge pricing is much different, especially if the user has to find out the pricing when they arrive at the restaurant. Ride sharing apps fundamentally sidestep this because you see the surge pricing without incurring a cost, and you can compare to competitors easily.
But with all the restaurants wanting more mobile orders, this may split the customer base in weird ways.