This sounds like an assigned project. I'll offer some thoughts or questions -
1. What is the "sound" or do you get to choose that?
2. Is the measurement done once or is the measurement supposed to be continuous?
3. What will you display? Time, speed - what units?
4. Will your apparatus be arranged so that the "sound" source is closer to Mic#1 - with Mic#2 a meter further away?
5. With #4 above in mind - what kind of signal do you have from Mic#1 - what do you have from Mic#2? You'll probably need to amplify them.
6. You might use Mic#1 to start a timer - Mic#2 to stop it.
Hopefully this helps get you started.