Trinity is open 9-5, Monday through Friday and in the morning of the first Saturday of the month. Holidays can affect hours but they are very good about posting on their webpage and FB.
Because of the limited hours, we try to help each other out. If you are having trouble making the work day window, I recommend dropping a note and seeing if anyone is swinging by soon. I can’t always guarantee a helper-buddy, but more often than not you can find someone. If you know what you want, after checking in that someone can do a pick-up for you, you can call Trinity and pay over the phone while letting them know the name of the person swinging by. If you need to browse the store personally, try for the first Saturday. I believe American Ceramics in Fort Worth has more frequent/longer Saturday hours. You can also buy all sorts of clay online but shipping can be $$, :).
Edit: I wasn’t exactly clear up there, my bad, but I’m volunteering to make a run for ya if you just need a straight p/u, I can go Thursday.