What's the best route to go from Paris to Mont Blanc? How much time should I allow?
Figure 7 hours. The easiest are a couple of TGV a day to Annecy, then 2 more trains the Chamonix-Mont Blanc. The fastest is a 6:11 pm TGV to Bellegarde then a bus direct to Chamonix. 5 hours and 39 minutes gets you there just before midnight.
How to Look Up Train Schedules Online gives you the DB train schedule link and tips for using it.