Timing in wince7

Currently I use the Colibri evaluation board v3.2 with the Colibri T20 that supports the wince7 operating system then the question I have is about the hologe, I have a Qt application which uses the QTimer library, so when I run the timer for a minute I notice that it has a significant delay of 10 s to 15 s. I d’ont know where the problem is.
I use the external clock.

@Soufiane151: Could you please check if you use the latest image 2.0 final? Are you using our pre-compiled QT version we have on our developer website?