If you want to have a look at the MX track [bear in mind it's a work in progress] google in "youtube 2010 masters old bikes"
scroll to "videos for 2010 masters old bikes" Click on 019benlee019 and youcan choose "old bike col" ,"modern bike "or "branch ball" [for a laugh.].
It's about a 2m 20sec lap for an old rider on a "pre75 bike,and 2m for a fast rider,so the pre75 races of 6minutes plus a lap will be a 9-10 min race for the average rider.Evolution races of 8min plus a lap should be 10-11 mins.