Can my staff see each other's hours on the POS?

No. The device only tells a person whether they have just clocked in or out. The hours themselves are on the dashboard, under Reports → Hours worked, which anybody with a dashboard login for your restaurant can open. A four number PIN is not a dashboard login, so a cashier who only has a PIN sees nothing. If you want a manager to check the hours, give them a manager login under Settings → Team. Only the owner or a manager can correct a stretch.