It's been a few years since we last stopped at 4 Vents, but from what I recall the local train station at Tournan-en-Brie took approx 35-40 minutes into Gare de l'Est as long as you take the quick train. We once got onto the slow (local) train by mistake, yes we got to Paris in the end but we seemed to stop at about 20 stations and it took ages. Nice site though, good location for driving to Disney too if that's your thing.