If you can do some post-processing, you can use semi-period measurement. This measurement returns separate values for the high and low pulse widths of a given signal. By summing up pairs of measurements, you can get the period for the signal. Every other measurement, will be the pulse width measurements. There is one catch though, currently there is a known issue with DAQ 7.3 where the starting edge cannot be determined. A workaround for this is to use the arm start trigger functionality of the TIO to begin on a rising or falling edge. There is an example that is very simliar to what you want to do that ships with NI-DAQ 7.3 called "Meas Duty Cycle-Buffered-Finite.vi" The only thing you should have to change about this example is the processing on the data from the Read VI.
I hope this helps!
gus...