I haven't actually dived into the scheduler to look at it. I'm not sure if it threads or if it is basically splitting the IterativeRobot style command loops between the commands. We've never done anything particularly timing-intensive (yet

) so we never had to look. (that's why I added the quotation marks, hehe)
EDIT: The cookbook says commands are accessed around every 20ms. It doesn't mention anything about priority, though.