When i was there, a lap of the red took me 85 mins
http://app.strava.com/rides/2934581 as proof ;) (and that was my first ever time there)
It’s hellishly fun, and it’s not that tiring as there’s a big old descent at the end. Oh, and spooky woods at the top (i think) is hellishly fun. The first climb does however, go on, and on, and on, and gets steep in bits. Just blast up it, it’s fairly straightforward.
Spent an afternoon there playing on the jumps, then i did glentress the next morning, and then a DH afternoon at inners. All on the same bike :D (after fort william was cancelled due to massively strong winds)
I rekon you can get a lap of glentress done, starting at about 9:30am, then go the cafe for lunch and cake, then a lap of inners easily within a day. You’ll even have time to be back at the pub in peebles at 5pm for an all nighter!