Duration wasn't changed, count was changed.  It is just a matter of how we were keeping track of shares on the backend.  This is mostly due to changes today for the following:

Worker stats are updated.
You should now see (on the stats page) your reject rate per worker, and stats coming from the stats page are now a ~15min average (instead of 5min average), in an attempt to have fewer people email me telling me their hashrate jumps around a lot.