Well the form and deposit went in before Christmas and I now have my receipt and rider number.
For any others thinking of this and filling in the entry form, once you've removed your arms from the straight-jacket, I opted for registration 2pm on Sat 25/7 and a start time of 8am Sun 26/7.
I also ticked the box marked slow after Dominic's comments about the moral boost of catching slower riders, and all speed zones had the same maximum anyway. Having read the small print I think it'll be a real mixed bag as they are going to start a mixture of speed groups at 15 minute intervals within each start time block so this effect will probably be lessened, but hopefully with some people always somewhere 'round about which ever bit of the country I happen to be in at the time.