I really just think it's luck of the draw - as far as I know they are supposed to arrive about every 20 minutes? But (hope this makes you feel better) I have got the VEA three times now I think, from CDG to DLP, and every time there has been one waiting there when we've gone to buy our tickets! Often they seem to park up and wait a few minutes to fill it up, so if you're the first one on you might be waiting a while, I guess, but at least it's nice to be on it and know you're all sorted!
If you're getting on the shuttle at 10.30am ish, you should have no problems at all, I'd guess. The only time I've had to wait is once when coming back (travelling from Hotel Cheyenne to CDG) and we had to wait about 30 mins, but we'd planned for that anyway. As long as you leave plenty of time on the way back, you shouldn't have any problems at all
