I have a stream with U3HV channels 0,1,8,3. It takes about 330 ms (0.33 seconds) to start the stream in labView 2014. I see other posts with much less latency to start stream. No error is indicated. Scanrate is 5 kHz. This happens with Labjack example VI as well (see pictures). I could roll back to an older LabView if that would help to speed things up. Could it help to do a low level function call to start the stream?
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That overhead of 330 ms you are seeing is occurring in the UD driver. When starting stream mode (LJ_ioSTART_STREAM), the UD driver first flushes out USB stream data, configures stream mode and then starts it. The flush is causing most of that overhead but is necessary to clear out the stream USB endpoint data properly and consistently. I've checked with older versions of the driver such as 3.25 and the stream start overhead is there as well. The current UD version is 3.50.
If the delay is causing issues, consider starting stream mode once for a long period and use data as needed (note to consistently read data still) instead of starting and stopping the stream repeatedly.