Currently, the timeouts for notifiers are specified in milliseconds.
I would suggest refering to the link that is posted above if this is a feature that you think should be added. Otherwise, the release notes for the next version of LabVIEW RT will include this if it is a new feature.
I have not dug into the low levels of OSs and hardware lately but I suspect that technological limits will or are playing a part in this. I would not suprised if uSec timeout would actually consume most of a CPU just servicing the clock interupts (based on one instruction per clock cylce which I question adn 1000 instruction per interupt).
So this leads me to ask
"What cahllenge are you facing that makes a 1 uSec timeout something useful?"