http://www.rideastonhill.co.uk/about/times/
They close the gates at 4:30 and I’d imagine would get pretty pissed if you went and rode out of hours as there has been years of wrangling to keep the place open .
Worth a trip though mate, the red route is great fun, the other trails are pretty steep and tech and very slippery when wet. The xc loop though short is tough, again mainly due to the steepness of the hill.