I have an SD4 Auto MY11.

Gearbox is throwing in some rough changes, confused changes, sometimes seems to be a box of neutrals, sometimes almost stalls going into reverse. All symptoms I have read about on here which have resulted in new gearboxes.

Currently the symptoms are not present all the time, and sod's law it drove perfectly when I took it to dealer, but I know it isn't right. Resetting adaptive memory made no difference. Advice is to wait for it to develop further then take it back.

If this is the early signs of impending doom, how long will it take to develop to the point it can be diagnosed and fixed? 8 months warranty left, will cover 10k miles in that time.

Keep taking it back and getting the problems logged and their responses in writing. Will give you the leverage you need later on if it fails after warranty. (Coming) 2016 RR Evoque td4 180 HSE Dynamc
(Going) 2013 TD4 GS Auto - Santorini Black with black leather. Cold Climate, UK Lighting & Armrest Packs. Privacy Glass. LR Rubber Mats. Full size spare.
60 000 miles averaging 35mpg

(Gone) 2010 TD4 Manual GS - Stornoway Grey. Sold at 3yrs old & 64k miles. Final average consumption 39.2mpg.

A per flylr, keep dropping in and reporting it, then when it goes out of warranty and should totally fail you are on record of reporting it a number of times in the warranty period. I did that with a Disco TD5, I knew the gearbox wasn't right but the dealer said it was normal, three months out of warranty it totally failed, new gearbox F.O.C. p****d off with a Digital Keyboard Warrior

I am now convinced the gearbox behaves completely differently depending on ambient temperature. Up to 15/16c ambient (according to dash display) the gearbox behaves perfectly and is a joy to drive. From 15/16 up it often throws in the strange behaviour detailed above which had me worried about impending failure. Now I think it must be a software/sensor problem. Dealer not much help. Any ideas?

Take it to a different Dealer. If they're not too far try Duckworths at Market Rasen.
Make sure all your visits to the Dealer are logged onto the system in case of later failure.