If the times you would like to book for are unavailable or greyed out, it may mean that area is full or not available at that time. Please have a look on some other days which may also be convenient.
If the app is not letting you place an order or select dates for collection/delivery.
Refresh the app by quitting and restarting the app. If the problem persists, go into your settings and clear your cache. You will need to restart the app again.