Documents dated after the date of application

Hi all,

So I've just applied for ILR as a dependant of my parent's Tier 1 visa. One of the requirements is to provide 2 documents that show my residential address and dated no more than one calendar month before the date of application.

So I have two questions here:
1) Does one calendar month means 28 days or 30 days?
So for example, if I submit the application on 18 December, would a document dated 18 November be acceptable?

2) Would the Home Office accept letters dated after the date of application?