Whenever you purchase a preload it will unlock at a specific time in your region, normally 12.00am.
Xbox One can have it's region switched very easily, to enable you to purchase games from other regions. The main reasons one would do this would be so that they
Pay the RRP of that particular region, a tactic used to save money for those living in Australia and New Zealand etc
Download content that in not available in your region (I'm looking at you China)
To switch to a region that hits 12.00am before your timezone, so that you can unlock that preload early
Information on how to switch regions and purchase content can be found here

I cannot stress how easy it is to do this. If you were preordering this digitally anyway, this will add an extra 5 minutes max. to your purchasing time and the best thing is as soon as your preload download starts, you can switch it back to your original location. So easy!
To be able to unlock the game at the earliest times, you are going to want to purchase from these countries, starting with the country that will unlock it the quickest for you

New Zealand (UTC+12:00)
Australia (UTC+10:00)
Hong Kong SAR (UTC+08:00)
London (UTC+0.00)
New York (UTC-05.00)
Los Angeles (UTC-08.00)

according to time map found at [ Register or Signin to view external links. ]

Let's assume that everyone is going to preorder the NZ version, as it is the earliest.

If MCC unlocks at 12.00am 11the November in NZ, it would be (roughly) the following times in these zones:

Australia - 10pm Eastern, 7-8pm Western (Depending on daylight savings) 10th November
Hong Kong - 8pm 10th November
London - 12pm 10th November (half a day early, potentially days early if EU are not getting until 14th November)
New York - 7am 10th November (17 hours early!)
Los Angeles - 4am 10th November (20 hours early!)

The above times are based of the assumption that the game will unlock at 12pm in each area (west,east etc.) however this may not be the case, but the above times are still accurate.

There are a couple of downsides to purchasing through the New Zealand Region, which are
You need to add Credit Card details, you cannot pay by paypal at all, points cards need to be purchased from New Zealand
You need to pay New Zealand's RRP for The Master Chief Collection. New Zealand are known to get just as ripped off as Australia when it comes to pricing. The NZ RRP looks to be $109.95NZ, which roughly converts to $86USD. (Other countries can enter their conversion rates via [ Register or Signin to view external links. ] This is the price we pay to unlock the game at it's earliest possibilty ;(
(You can purchase the game from the Hong Kong Region and it will download 2 hours later than the NZ version, however will be significantly cheaper. Probably around the $45 - 50USD mark. I would not recommend using the Hong Kong marketplace as it seems to be heavily filtered and censored, so MCC may not ever release on the 11th November there.)

We will have to wait and see when the preload says it will unlock and take it from there. My advice would be to not purchase the preload until you are happy with the Region you are purchasing it from and understand when it will unlock.

The above times are based of the assumption that the game will unlock at 12pm in each area (west,east etc.) however this may not be the case, but the above times are still accurate.

There are a couple of downsides to purchasing through the New Zealand Region, which are
You need to add Credit Card details, you cannot pay by paypal at all, points cards need to be purchased from New Zealand
You need to pay New Zealand's RRP for The Master Chief Collection. New Zealand are known to get just as ripped off as Australia when it comes to pricing. The NZ RRP looks to be $109.95NZ, which roughly converts to $86USD. (Other countries can enter their conversion rates via [ Register or Signin to view external links. ] This is the price we pay to unlock the game at it's earliest possibilty ;(
(You can purchase the game from the Hong Kong Region and it will download 2 hours later than the NZ version, however will be significantly cheaper. Probably around the $45 - 50USD mark. I would not recommend using the Hong Kong marketplace as it seems to be heavily filtered and censored, so MCC may not ever release on the 11th November there.)

We will have to wait and see when the preload says it will unlock and take it from there. My advice would be to not purchase the preload until you are happy with the Region you are purchasing it from and understand when it will unlock.

Regarding paying (potentially) half price for MCC digital version:

Well, if you have a friend/roommate/relative, you can combine this digital preload with the Xbox One sharing program, also known as a licence transfer and it will enable two people to play 1 copy of the game simultaneously on different xboxes on different gamertags and only pay the one fee. Essentially, you could split the cost in halves!

There are certain limitations and things to this, however it works perfectly for close friends/siblings etc that live in the same house or with someone who you trust 100% as it does involve signing and out with XBL Gold accounts.

More information on Xbox Sharing can be found on youtube here. There is also an article on the xbox website itself here.

Feel free to whack your questions in here, so I and others can try and answer them. I don't have all the answers, however I thought this thread would help at least a few loyal Halo fans unlock the game earlier (bad luck NZ players, you have to wait til midnight ) as well as save a few bucks.