I'm doing a program that saves the date and time into a file (with another
things in the same line). Then this file is going to be open with a program
in C.

The problem is with DayLight Saving Time.

How can I put "something" to put it on?
When labview changes it?

I believe the simplest solution is to change the Windows setting.  You
can turn off daylight savings time.  Even better, you can exclusively
use UTC  (universal coordinated time) or equivantly,  GMT (Greenwich
Mean Time).  The msdn link below discusses how to make these changes.
Your last option is to move to parts on Indiana.  (haha)

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/tdhe...