I took part last year. The timing is alright because you have about 3 hours for each theme. But it's even better if you have your own transport because traffic on Saturday is usually very busy.
Last years' event, about 600 pre-registered for the competition. Based on the photographs submitted during this pre-registraion round, they narrowed down to about 200 participants. In the end only about 150 turned up.
I have notified the organisers via email about the error in registration page. There's supposed to be an entry where you submit a original photograph for pre-registration.
Do take part. It's fun! Last year, we're all given a free photo-vest and McDonald vouchers too.