It's back to 3pm, according to official sources:
http://www.manutd.com/news/fullstory.sps?iNewsid=204850&itype=1020&icategoryid=0
Manchester City (H)
Manchester United v Manchester City, Saturday 10th September, PLEASE NOTE THE KICK OFF TIME FOR THIS MATCH HAS BEEN CHANGED TO 3pm
All tickets have been sold.
http://www.mcfc.co.uk/default.sps?pagegid={DBD12D53-8346-431D-A04F-5D0F8664DE80}&newsid=230570&siteid=&pageno=&newscategory=1051&frommonth=6&fromyear=2005&tomonth=8&toyear=2005
27/08/2005 12:20
The Club have also announced today the change in kick off time for the first derby of the season. The Old Trafford fixture will now kick off at 3pm on Saturday 10 September and not 1pm as previously stated.