I can remember many, many (many) years ago races would start at 2 or 3 pm on a Saturday afternoon. This was when traffic was very much lighter than it is now and road closures didn't happen. As road traffic increased over the years, races were moved to Saturday mornings and then Sundays. Now it seems that with a couple of rare exceptions only Cross Country races remain on Saturday afternoons. The earlier and earlier start times are purely down to traffic and where road closures are required, local authorities, highways agency and the police prefer that the race is over and restrictions lifted as early as possible. 10am isn't too bad; I know of several races with start times of 8.30 or 9.00. As mentioned further up this thread triathlon start times can be as early as 6am. It is difficult for people relying on public transport but sadly it is a sign of the times; the only way around this is for organisers to provide more off-road or trail races where the impact of traffic is negated and leisurely start times can be accommodated. I ran a 10k (off-road) in Richmond Park last weekend with a 10am start and barely a car in sight.
You need to be clear on whether pacers are running to race (gun) time or chip time. If a pace group catches you up and you stay with them be aware that their time may be less than yours if they crossed the start line behind you. It may be better to try and find your pace group before you cross the start line even if it means dropping down a pen or two (not sure if this is allowed though). If running a sub-3, 3.15, 3.30 etc is really important to you it is worth checking.
I wasn't sure what a 'Jedward' was so I checked out the link provided. It told about two young men in strange outfits and unusual hairstyles who had apparently run a marathon without any training. It looks as though they were doing what my mother calls 'showing off' so they are probably publicity seekers. I could see no mention of their finish time.
I am sure it is possible to 'complete' a marathon with minimal or no training; there are plenty of finishers in 7 or 8 hours in London every year; which is walking pace. This opens the can of worms which is whether there should be a cut off time of say 5 or 6 hours. Beyond that it really isn't 'running' a marathon.