hi,
Have you tried saving the current time in Arduino Measure? Every time voltage change = true write current time to a spreadsheet file? You can use excel afterwards to get the difference.
Or you can save the current time to labview variable, but be careful of race conditions!
Or you can use two timestamp references that would be input the measure VI: current and previous. Every time voltage changed = true, set previous value = current value and current value = NOW. subtract them to get the value you want and save it to a file from there.
Also, using the global voltage change boolean is asking for trouble in the form of race conditions. Use the reference to the voltage change boolean on the front panel of main for everything, and make sure that only measure writes and all the rest read.
I'm still not sure I understood your code, so my apologies if I missed something obvious.