If you are doing in person, you pay when you book which can be 42 days before the appointment and you pay the fee as of the day you paid (not the appointment date).
I get to book on Monday! It's £590 extra for in person and £75 extra for some more desireable time slots!
So... if my entry on a marriage visa was February 1, 2013, and my first FLR (M) was June 5, 2013 (that was my in-person appointment date), I go with 5 years from June 5, 2013, as my 5-year start date, right? So i can apply up to 28 days before 5 June, 2018... May 9th, or thereabouts. And I can book an in-pwrson appointment up to 42 days before that... so it is
possible that I could pay before the fee increase, too (assuming it's not early again). That means instead of paying the fee increase, I could pay for in-person instead, and it wouldn't cost too much more that a slow application after the anticipated fee increase. Yes?