Hello Kelly! Essentially, it sounds like you are wondering how accurate the wait functions in LabVIEW are. The timing accuracy of a Windows-based computer is typically 1ms, so at first glance the answer to your question is approximately +/- 1ms. There are several things that can affect the timing of a VI, however, such as other applications taking processor priority and other functions inside your VI taking longer than the wait time specified. In general, if you are needing accurate timing, take all of your other operations 'out of the equation' (i.e. remove them from the loop if possible).
A lot of the time, very accurate timing can be done at the hardware level. Depending on which hardware you are using, you may have the ability to use an onboard clock to control your analog output. This is known as 'Waveform Generation.' See the NI Developer Zone tutorial on <a href="http://zone.ni.com/devzone/conceptd.nsf/webmain/3B13FEA05458E2E286256802007B91DE?opendocument";> Waveform Generation</a> for more information about hardware timing.
