At checkout the system re-checks the order time: it must be in the future, at least now + Order Buffer Time, and inside one of today's windows. If it is not, Sprwt automatically replaces it with the next available time (now + 5 minutes snapped into the next window). If no valid time remains today, the cart cannot be closed and the customer sees the order-time error ("Please select a valid order time for date!"). Changing the time manually to something invalid returns "Invalid order time provided!" and keeps the previous time.