The time zone is an artefact of conversion from "instants" to a human-readable date-and-time in some calendar.

Computers do not like human-readable formats (not as much as humans, at least), so they usually store instants in a zone-neutral format. For instance, in the NTFS file system, time stamps are stored in UTC.

Hence, the file time modification is stored properly as long as whoever modifies it knows the current time. If your Windows system displays "13:19" and believes to be in the GMT-5 time zone, then it infers that the current instant is "18:19" in UTC, and writes as much in the NTFS entrails. However, if the OS displays "13:19" but believes to be in the GMT+3 time zone, then the OS is off by eight hours, even if, for the human looking at the screen, things seem fine.

Another point is that the file modification time is a property of the storage system in which the file is stored, e.g. a file system. When a file is "sent", then that time does not necessarily travels with it. Some archive formats (e.g. Zip) embed the file modification time along with the file. This does not apply to a file sent "as is", attached to an email, will not come with a file modification time.

This is for an Excel worksheet. Data is entered or modified in column A. The macro automatically enters the date/time in column B. The macro then sorts column A & B by column B, putting the most recent at the top.

Enter the following event macro in the worksheet code area:

Private Sub Worksheet_Change(ByVal Target As Range)
    Dim A As Range
    Dim AB As Range
    Set A = Range("A:A")
    Set AB = Range("A:B")

    If Intersect(Target, A) Is Nothing Then Exit Sub
    If Target.Count > 1 Then Exit Sub
    Application.EnableEvents = False
        Target.Offset(0, 1) = Now
        AB.Sort Key1:=Range("B1"), Order1:=xlDescending, Header:=xlNo, _
            OrderCustom:=1, MatchCase:=False, Orientation:=xlTopToBottom, _
            DataOption1:=xlSortNormal
    Application.EnableEvents = True
End Sub

Because it is worksheet code, it is very easy to install and automatic to use:

1. right-click the tab name near the bottom of the Excel window
2. select View Code - this brings up a VBE window
3. paste the stuff in and close the VBE window

If you have any concerns, first try it on a trial worksheet.

If you save the workbook, the macro will be saved with it. If you are using a version of Excel later then 2003, you must save the file as .xlsm rather than .xlsx

To remove the macro:

1. bring up the VBE windows as above
2. clear the code out
3. close the VBE window

To learn more about macros in general, see:

http://www.mvps.org/dmcritchie/excel/getstarted.htm

and

http://msdn.microsoft.com/en-us/library/ee814735(v=office.14).aspx

To learn more about Event Macros (worksheet code), see:

http://www.mvps.org/dmcritchie/excel/event.htm

Macros must be enabled for this to work!