You'll be fine, although i've not been there for a while, it's not a technical track and a hardtail will be fine. At least then you can mess about on the singletrack
itll take you a bit longer than 30minutes, used to ride there from lydney most weekends, the train station is just outside lydney.its slightly uphill all the way but isnt too bad on a hardtail just pump your tyres up hard. wikid trail used to cain it on a hardtail most weekends and loved it..
Sadly, the first train is at 8 am and it will tale me 5 hours kust to get there by train with 3 changes. As well as my English exam next day. I dont think i could make it. I will definetly go on a next one. Or maybe just go there just for a ride. Sounds interesting.