Can i postpone my biometrics? For ILR purpose

[globetrotter_ks]

Hi i was issued tier1 visas ( its 3+2 yrs ) in India on 17 Feb 2009 but i entered the UK on 6 Aug 2009 i.e late entry by 5 months and 20 days. Have applied for 1st extension on 16th feb 2012 and recvd biometrics letter dated 19 march saying that within 15 days i have to book appontment. Now for ILR it says that they will consider only if the applicants have entered the country within 3 months or else they will have to go for another extension which will cost me extra money later and stress. I checked the appointment dates on ukba website and appointments are available in brighton, birmingham ( out of london centres) for april 2012 end and may start.

Is it possible to book the appointment so late? will the UKBA question me that why i have booked it for a late date and out of london centre or why i did not go to the nearest post office in London?

I want to delay it so that incase if the outcome of my current application is late by 5 months and 20 days( as i entered the UK late) i will be benifitted and i wont have to go for another extension and can directly apply for ILR later. plss advice guys.