Auto Update Statistics Duration and Interruptions
You can grab this data with the Auto Stats Event Class with SQL Trace.  One of the event's data columns is Duration.  As per the referenced BOL documentation above, here is a quote:


  Duration: Amount of time (in microseconds) taken by the event.


That should give you a pretty good idea when/how long auto stats is taking.  If you are seeing a lot of performance-halting auto update stats (synchronously), you could consider utilizing auto update statistics async.  Turning this on will tell the query optimizer to not wait for statistics to be updated in order to continue compiling the query.  This is one solution in order to prevent the direct interference of stats updates, but of course you're sacrificing fresh statistics for that particular query compilation.

For more information on this, please see the MSDN reference on Statistics.