|MadSci Network: Earth Sciences|
The short answer to your question is that the length of day (LOD) changed on the order of 2.7 microseconds (0.0000027 seconds). There is a USGS report on the earthquake.
The LOD changes from day to day due to a number of causes. Seasonal and monthly effects cause changes on the order of milliseconds (0.001 seconds) per day. The LOD can be measured reliably with an accuracy of about 20 microseconds so the 2.7 microsecond change is below the level of direct observation.
B. F. Chao at NASA Goddard Space Flight Center and R. S. Gross at Jet Propulsion Laboratory published a study on the effects of earthquakes on the LOD. They concluded that earthquakes tend to make the earth more compact, speeding it up and decreasing the LOD. Their report is available online.
Other links you may find useful are the U.S. Naval Observatory, the USGS and the International Earth Rotation and Reference Systems Service. The IERS site requires you go through the main page. On the IERS site, click the web site map and find the “Universal Time (UT1) and Length of Day (LOD)” link.
Try the links in the MadSci Library for more information on Earth Sciences.