you have to apply b4 your visa expires !, but you cannot apply too early,,
from the guidance notes..
you should apply before the end of your/their permitted stay in
the UK when you are nearing completion of the 2-year qualifying
period required by the Immigration Rules.
Please do not apply more than 28 days before completing
that period. If you apply earlier than that, your application
may be refused. If that happens, we will not refund the
fee and you will have to pay again when reapplying.
For visa holders only. If you obtained a visa but delayed
your journey to the UK by several weeks or more after the
date from which your visa was valid for use, you may need
to apply for an an extension of stay on form FLR(M) to make
up the 2 years. If you are in this situation and need more
advice, please call 0870 606 7766.[/I]
you don't have much choice, no point in applying for flr because of 1 day, just post it when i said, and you shouldn't have a problem , am sure they will use their discretion