Thanks for the answers and sorry for the late reply guys, much appreciated indeed. So, what you are saying is, I can apply 28 days before my 5th anniversary (starting from the day of first entry) but I can show my absences for the 5 year period which is starting to countdown from application day+28 ...

I entered UK 10 months after getting my visa (HSMP at that time). Do you guys think I can show the 90 day part of it as absence? Or it won't count since it is more than 90 days? So, I entered UK on 13/02/2009, can I apply on 13/11/2013? If not, how about the 28 day earlier rule? I should be able to ...

I wonder why the second extension is for 2 years. Your visa was for 2+3 years, so I thought the second extension would be for 3 years as well... Anyone with a different experience?