I'm sure someone else will be along shortly with more detailed information…but…yes, the ride from 1600 to Vallandry is pretty easy and yes ~30min. There is the nice little run down under the lobster pots back into Peisy if you go via Vallandry. Not ridden Val->1600, no point, down to Bourg back up on Funicular.
There's a great run(s) down to Bourg from Vallandry (there is also a way from Peisy but I can't remember the directions). We used a trail that left from near the recycling point on the road below Bar Maxim. It runs down to the valley with about a 1km ride to the Funicular. Forget whether the Cachet runs on Saturday, so you may be 'limited' to trails from 1600. Then the XC from 1600 back across to Peisy.