Hello jtaclas,
The description of the AO Wait's Update Rate input is:
update rate is the number of updates to generate per second. The default rate is 1000 updates/s.
In DAQmx you set the rate at which the samples are updated with the DAQmx Timing VI. If you look at the example Gen Mult Volt Updates-Int Clk.vi from the Example Finder, the timing actually comes from the waveform datatype that you are using for your output. You also could use the Sample Clock instance of the DAQmx Timing VI if you did not wish to use a waveform datatype and then you will have an input for "rate".
There is additional information in the tutorial
Transition from Traditional NI-DAQ to NI-DAQmx. The difference is that the AO examples described are continuous instead of finite, which is when you would use the AO Wait and DAQmx Wait Until Done VIs.
Please let us know if you have additional questions over this.
Thanks!
Laura