I created functions to manipulate dates easilly
In created 2 functions Date2Serial and Serial2Date which converts dates separated in day/month/year in a simple Integer in the same way as Excel or Delphi does.

With these functions, it is easy to add or substract days to a date or calculate the difference between 2 dates.

I added the code in the archive here:
http://nsis.sourceforge.net/archive/...php?pageid=450