The way you have your VI configured, the outer while loop will only run once. It will run, but will not be able to continue until the inner loop has completed. The inner loop will continue to acquire data until the desired time has passed. A this time a true will be written to the stop terminal on the inner loop, and then passed to the stop terminal on the outer while loop, stopping it when it has only run through one iteration. I'm not sure what you are trying to do, but my guess is that you want your second while loop to be outside of the first one. You can then stop them both by using a local variable or some synchronization mechanism.
Regards,
Ryan K.