Off the top of my head, there are 2 types of 20mph "restriction" - a 20mph zone and a 20 mph limit.
A 20mph zone requires terminal signs at the start/finish of the zone, and traffic calming measures (with stipulation on maximum distances between such measures).
A 20mph limit requires terminal signs and regular repeaters.
The signage on GSV indicates that it is a 20mph zone, and appears to have quite a few traffic calming measures (or at least have had when the images were recorded).
If "throughout the village" (where the repeater signs were being put up) is also a 20mph zone, rather than a 20mph limit, then there would appear to be no requirement for repeater signs, and presumably placing them would even be unlawful.
If the signage (including requirements for traffic calming measures) is defective, that might constitute a defence or defence strategy*. If the TRO is defective, then presumably there would be no 20mph restriction in law, so no offence could have been committed.
Were the camera van was parked is utterly irrelevant, and the requirement to serve a NIP on the RK within the 14 days appears to have been complied with.
Regardless of whether or not you have any defence to the speeding charge, you must name the driver by 28th May.
For speeds of up to 10% +9mph over the limit (so 31 in a 20 limit) you should expect to be offered an SAC. Received wisdom suggests that the s. 172 response admitting to being the driver would need to be received within 3 months of the offence, and the course completed within 4 months of the offence - so unless you have a reason for delaying, it would seem prudent to do so sooner rather than later.
You are far too far from timing out for delaying to be a worthwhile strategy to cause a time-out.
The only other common reason for delaying is if you were trying to get advance sight of the photo(s) on the ruse of asking for them in order to help to identify the driver.
