In reply to Callumjnelson:
Good evening,
The Midi will be open, Brevent and Flegere will be open for a short while in October (but the exact dates escape my memory, I'm afraid) for the French holidays, the Grands Montets will be closed, I haven't got a clue for Le Tour or Les Houches, and Montenvers, malheureusement, will be closed until December because they are going to try and move the bubble lift to slightly further up the glacier. The lack of Montenvers is, obviously, a bit of a hassle for peak Grandes Jorasses season.
Lift information can be found here:
http://www.compagniedumontblanc.fr/fr/remontees-mecaniques-chamonix
With regards to your second question... where exactly would you like to walk to? The walk to the Albert Prem hut can be anywhere between 2 and 4 hours depending on fitness and kitness, expect the walk to the Argentiere refuge to take somewhere around 5-7 hours, the walk up to various bivvy sites in the Chamonix Aiguilles might take around the same unless you are super fit and travelling light... and getting to the Envers hut without the Montenvers train will probably take a whole day.
If it's a late summer and sunny rock in the Aiguilles Rouges is the ticket, then walking up from the valley with a nice light rack might take you as little as 2 hours, more likely 3 or 4.