Measure passing time between to rising edge in analog inputs

Hello guys, I need a little help!

I work with a National Instruments Data Acquisition Device and I use the digital multi meter (DMM) part of the device with two capacitive sensor ( I use this part of the device because i work with industrial voltage). They are come into the same input.
I use Mydaq Assist to visualize when the sensors get sign and I put a Waveform Chart and a Led to see it works.
I would like to measure the passing time in seconds between two rising edge and i need some help to solve this problem.