Hi Peter!
Thank you for your attention. After a thousands of experiments I know what to do now. Your idea to use the gate mode is working fine! Now I can get true results of measuring. I can also synchronize to the pulse, but it looks so simply that you never belive how difficult it is... I have found the time to compare LOW and HIGH pulses' time too. It is very close to the end of coding (I hope).

Jacek