You'll have to wait until December,I'm afraid - the Act requires you to have been physically
in UK on a day exactly five years before you submit the application. There is no flexibility over this.
I think the thing to bear in mind is that, with Immigration applications, you have to apply before the existing permission expires, so that you don't have any gaps when you are here without permission. But with Nationality applications, you apply after you have completed the requirements laid down in the Act.
paul