Do staff have to open a shift before they can clock in?

No. Clocking is on the sign-in screen, before anything else. Tap the clocking button first, then your name, then your four numbers, and the screen says you are clocked in. A shift is a separate thing: it belongs to the drawer and is opened by whoever counts the float. So a waiter can clock in at four on a waiter phone while the counter shift is not opened until five. Clocking out works the same way at the end, on any of your devices.