Posters are more likely, I think, to be familiar with Hanyu Pinyin romanization, which is worth (IMHO) the effort to learn. I believe you’re talking about zi4zhu4can1, or cafeteria-style places. They may be open for limited hours at peak meal times, e.g. 11:30 a.m. - 2 p.m., and 5:30-8:30 pm. The best thing to do is to find the ones nearest you and ask what time they’re open. They will often write this on the door, so have a look.
I have never seen any of them write that on the door… in fact sometimes I go their during their “normal” business hours and they’re not open… I don’t know why. Only way I can know their operating days/hour is by going there on a regular basis.