From what you are saying it seems that you are relying on the computer's clock to handle sensor measurements, which is basically an incorrect solution due to hardware limitations of the PCs. On the contrary, since you have a daq board to use, you must perform this measurement entirely inside the board.
According to PING documentation, "The PING))) sensor provides an output pulse to the host that will terminate when the echo is detected, hence the width of this pulse corresponds to the distance to the target." so your problem seems to reduce really to a pulse width measurement, a task usually demanded to board's counter.
Basically you can use PING pulse as a gate to drive a counter which counts only when the gate signal is high, and given the 20 MHz clock of internal timebase you should be able to measure the pulse width with adequate precision.
I suggest you to search inside samples folder for pulse width measurement daq examples which should give you a good starting point to develop your application.
