When to apply for ILR

[Pigeonfox]

Hello,
I am new to this forum and I'm really desperately seeking advice on when my husband can apply for ILR.
Firstly, he entered the UK on a fiance visa.
The he got his first spouse visa/ leave to remain for 2.5 years on 09/02/16.
He renewed this on the 17/07/18 and got another 2.5 years.
Therefore his current leave to remain for 30 months will expire on17/01/21. But he won't have been in the UK for 5 years until 09/02/21.
Which of these dates does he apply for ILR up to 28 days before?
If he has to apply up to 28 days before 09/02/21 but not outstay his 30 months, that means he only has a 5 day window to apply! Which will be difficult as we need to apply at a premium service centre and the appointments can be hard to get.
Thanks in advance.

[zimba]

Either apply within 28 days for ILR or apply for extension via post and vary it later to ILR when eligible.