I know that for the 2010 game, qualifying times could be edited with the database.bin file, but then you could only change how fast the entire field was not each driver. I am not sure how things work with 2011 though...
Before you start though, I think we need more information:
Are you playing career or grand prix mode?
which car are you in?
what are the other difficulty settings?
what laptimes at what track?