As another local, and a guide on the mountain http://www.mtbguiding.co.uk , I’d like to echo other opinions here.
1. Pushing up at any time is unlikely to cause a problem per se, and I’m not sure about counters and wheels? But the problem is that a. you will definitely be descending a busy path – no fun for you or them and b. The walkers you pass will obviously realise that you were on the mountain a lot earlier than 5 and that will almost certainly form part of any complaint.
2. Yes, it’s voluntary but anybody who flouts it is just sticking 2 fingers up at all mountain bikers as we will all be banned from the mountain altogether.
3. A suggested route would be to start at the Ranger at whatever time you like. Go up and over Bwlch Maesgwm and down Telegraph Valley at whatever time you like. Then head back up Snowdon at around 5pm from Llanberis. You’ll top out by 7 and can then descend the Ranger back to the start – probably by 8, which isn’t too late to get some grub or check into accommodation.
Enjoy