Both AO and AI VIs that you mentioned are software timed VI meaning you are not performing the operation based on the hardware clock (not very accurate timing). You should use hardware timed VI e.g "function generator" example in labview and "Cont Acq and Graph Buffered.vi" example in labview. Another good thing is that those examples perform buffered operation which involves downloading/fetching the data to/from buffer and then start operation on the board.
A Rafiq
National Instruments