Count the delay time between two signals

[Water1]

Hello !
I use PCI-6115 to acquire two signals
One is excitation signal ,the other one is response signal.(see delay time.jpg)

Now my question is that how to count the delay time between two signals?

I also write two vis to count it ,but it seems that is difficult to count the delay time .

Who know where am I wrong ?

Thank you in advance !

[Water1]

two signals are spike train.

For delay time.jpg ,yellow signal is excitation signal, red signal is response signal.