I think it's a matter of expectations. When I go to a restaurant, I'm OK knowing the price is X, but today (or right now due to whatever) the price is lower, but I don't want the "surprise" the price is X+Y when it's usually X due to something, e.g., shortage, high demand, or time of day.

If restaurants want to have time of day based pricing, I'd be OK with the base price being the highest price, with discounts during other parts of the day. For example, early bird specials have always been a thing (lower prices late in the afternoon before the evening rush). What I find objectionable is there being an unknown, unexpected, up charge based on anything, time of day, day of the week, phase of the moon, ... It's objectionable even when the up charge is mentioned when I arrive due to the overhead of having to go somewhere else.