The registration closing tab is where you can set the date / time that the registrations will automatically close.
From then onwards, the page is not available for public use and a message is shown on screen - 'Registrations Closed' - we generally recommend that you do not use 00:00 please use either 23:59 or 00:01
The text box allows you to type a message which is then displayed on the screen to provide them with further information once the registrations now been closed. For example if you have on the day registrations you could enter a message about the times and location of where on the day regurgitation will take place.
