Chris Page posted this official announcement at the iRacing forums regarding downtime to the service Wednesday, 27th April.
New build!
Wednesday, 27-APR-2011 GMT
EST(-4) GMT AEST(+10)
0500 0900 1900 No New Hosted Sessions
0900 1300 2300 Service Down
1300 1700 0300 Service Up
All times are subject to change.
EDIT - Moved from Tuesday to Wednesday