Yes PAT, that's right. If you started living in UK during November 2009 you can apply for ILR during October 2011 . Just count 24 months (November 2011) minus 28 days from the actual date in your case. (October 2011) That will be fine.
The 27 months is the expiration of the visa. You could apply anytime up to the expiration (from October) but it's better (I think) to apply early as possible.
I would suggest you take a look at the UKBA website and the ILR forms and guidance just so you can be prepared to comply with all requirements. You really should have no problems at all.