Hi Leo,
The problem is that Capacitive Touch Sensor TTP223 has a response time in best case at 60ms to 220ms.
So when I have to compare the time of both sensors which are less reactive than the real signal the result of this comparaison is less accurate than it should be ( if i do it with push button instead of capacitive touch sensor).
So I think , if I use a Capacitive Touch Sensor which has a fast response time the result of the comparaison will be more accurate and will reflect more the reality ???
thank you for you help! 
Regards