Shopping in Taiwan

You know, that little Mom and Pop store in your neighborhood that you cruise by on your way to work each day sometimes has just the stuff you're looking for. But, you're in a hurry. You rush in and leer at the things you need. Checking around you see a TV on, and a few friendly seated faces, and so you say "Sunday?". "Eh? Ahhh... Dengsha...", and you curse yourself for not having studied Chinese more.... Now you're talking to a very nervous woman who's obviously been pressed into translation duty; an older relative peers at you from the back. Wait a minute longer. Class is starting soon. OK, now you're facing the... owner? Not sure. You manage to get to Sunday by holding up the seven sign with your hand... OK... but what time? They say they will be open, but... is it just for you? No? Yes, I'll come, but... you are open on Sunday? Now, your class is starting... you look at your watch... Saturday?