In reply to nk: Voie Frison Roche is good, six pitches-ish, about a 6a crux, on the Brevent, but popular. Get the first cable car to the top and run down from there to the start!
We had a more leisurely approach to it, going up late in the day, so by then the route was empty, camped afterwards and did another route the next day (Crakoukass). Maybe you could do this but not camp, deliberately miss the last car and walk back down into Chamonix. The walk isn't bad and I've done it a number of times but it might not work for your commitments.
The front face of the Index has a number of bolted lines which you could do in half a day, okay routes but nothing special. 10 min approach from the lift. They avoid the crowds until you meet the standard route at the top.
Loads of multi-pitch routes north of the road near Vallorcine area and towards the Swiss border, some quick access, climb as far as you can, then ab off when your time runs out. Maybe an idea. I remember Slyvie Phobie being good (Nice 5/6a for a number of pitches than 6b+ high up, but you can A0 that bit)