ILR SET (M) 5 years route

Hi there,
I am new to the forum and i hope i can be forgiven if i have made a mistake by starting this topic.
A brief history of my immigration status.

15th Nov 2014 (Granted spouse visa) 5 year route.
16th Jan 2015 (Entered UK on spouse visa)
16th Aug 2017 (Granted FLR/M) 5 year route.
FLR/M : Valid until 17.02.2020.
I would like to ask a few questions please :
(A) when is the earliest i can apply for ILR (SET/M)
(B) In my FLR/M approval letter it stated i can be refused if i apply before 28 days of the lapse of my current visa. (17.02.2020).
(C) Since Dec will be Christmas period, my spouse and i will be paid early. Even if we apply on the 22nd Jan which is within the 28 days time period. Our payslips will be more than 28 days old by that time. Can you please point me to the government link where it states i can apply within 28 days of the time i completed 5 years in UK as a spouse?

You can apply no sooner than within 28 days before the 5th anniversary of the date you entered the uk, so 16 January 2020 minus 28 days.