Yeah, think Cadir Idris is north of the loop, so if you climb up the south face (Cad West is at the bottom), you’ll have a good chance of seeing passing traffic if the incline allows – they fly west down the valley over Tal Y Lyn lake then either turn left to do another loop or climb up and away (most things I saw did two laps, the climb out of the lake is one of the exits), so I would imagine, even if you don’t get a close up view (they are VERY low when they go through Cad!), you’ll see them on the way in or out. 🙂
I didn’t find the timetables to be of any use, there were “scheduled” sessions with nothing happening and planes flying the loop outside the specified times. The impression that I got from overhearing geeks was that there isn’t a way of knowing ahead of the day what’s going to be flying, but with the right connections and scanners, you could make an educated guess on the day (some chap near Mildenhall apparently posts on a plane spotter Facebook page when anything interesting takes off). I was happy just to head for the hills with my book, but then, I didn’t have a nine year old to entertain – I’ve no doubt there are some fully-geeked Facebook groups to stalk where you’ll get better tips, unless anyone on here has better info? 🙂