In the first game, the convenience store's hours were 7-11, a reference to the original hours of a certain popular convenience store chain. Even then I thought it was odd that that store had better hours than the upgrades.
Super T&Ts hours are ridiculous. what kind of supermarket closes at 8pm?
places like albertson's/tom thumb/kroger. 8pm may be a bit of an exaggeration, but walmart's really the only supermarket open in the wee hours.
personally, it makes perfect sense to me. the first upgrade is a convenience store. the final upgrade is a department store. do you know ANY department stores that are open as late as convenience stores are? you're trading later hours for a larger selection. if it's THAT difficult for you to get into the nooklings' store before they close, set your game's clock back a few hours.