What is the latest time that they still have steamed pork buns (they seem to run out later in the day)?

It varies depending on how busy they are each day. I would try to get there early because they seem to run out of some items after 2:00pm or so. You can also give them a call before going to see if they've run out of anything.

Call them to place an order

Yeah aboit 2 your done gor those buns.