Personally I suggest you do not make application 28 days before your eligible date.
This is only applicable to visa applications

You should take special care to ensure You comply with the strict rule here:-


Please note: You should also check that you were physically present in the UK 5 years (3 years if you are married to or in civil partnership with a British citizen) before the date that the application will be received by the Home Office or other receiving authority (see page 17 “Where to send your application form”). If you do not meet this requirement your application is unlikely to be successful, unless you were in the UK armed forces at that time.
It's an odd rule but it does get enforced.