The simplest method to achieve timed loop can be found at:
http://zone.ni.com/devzone/conceptd.nsf/webmain/E83351E12CD2D50886256B66006E4D15?opendocument
However, you can achieve your objective without even using timed-loop unless this is critical. I'll post a vi to show you another way to get it done.
I want to suggest you make the following changes to your vi: move write/lose file vi outside the loop and your data sampling vi should be inside the loop (again, this can be done in several ways).