Any store that sells stuff that you want can be a good place to dive. Grocery stores, bakeries, and health food stores are by far the most consistent producers. You can find something almost every single day at these stores. Other stores can be great too. ALL good diving spots.
Every diver has a preference.
Folks dive at all times of the day and night. I've found that these are the times when I'm least likely to be confronted at my particular stores. But, the deciding factor is that I have a partner to go with me at night. If you're diving alone, you may want to think twice. I have CAM to dive with me at night.