Hi Twiggy,
I don't have any answers to the questions you pose, but page 275 of the coffee-table book
Gallipoli. Untold stories from war correspondent Charles Bean and front line Anzacs talks about an Australian who invented a technique for firing off rifles by
"two bully beef tins full of water and a bit of string...it will pull the trigger as late as 20 minutes after it has been left'.Men were evacuated in small groups at first with the final Evacuation Days the nights of 18 and 19 December.
This book is an excellent day-by-day account of the campaign, and although from an Aussie point of view rather than Kiwi or British, covers the daily struggle to survive the snipers, artillery bombardments, thirst, etc.
If you read the most recent newspaper articles and
New Zealand Listener dealing with Anzac Day commemorations you will gain a lot more information. And there is the WW100 website as well
http://ww100.govt.nz/Spades