TLDR: I applied for ILR after my Residence Permit validity expired but within a grace period and was granted ILR.
My 2nd 2.5 Year Leave To Remain Visa was coming up to renewal in September, specifically 21/9/24 according to my Biometric Residence Permit. I began the application in May getting things ready and was advised that I could not complete it until I was in 28 days of the expiration. (Note: this advice was provided by a UK Visas agent, informational only and I have seen that advice contradicted stating I could have applied anytime after the 5 year mark (which would have been July 24). Regardless, I set a date to begin working on it in my calendar and put it aside.
When the calendar notification came up, I started to work on the application, only to realize, I had set it for the wrong date on my calendar. I was appalled to realize my residence permit was valid up until 21/9/24 and I was looking at it on 3/10/24! I frantically started searching out advice and ended up using a solicitor firm to help me with the application (I have always done them myself - both the initial one and the renewal and one 15 years ago when I was here for a short time).
They submitted the application the very next day - pending Life in UK Test and Biometrics. They put a placeholder in the Life in the UK test blank space to get it started. I studied and passed the Life the UK Test, first try on 17/10/24 and then went to Biometrics on November 3.
On 9/12 I received an email (well the solictors did), asking why there was a delay in the application. I didn't have an acceptable reason, as it was purely my mistake! I replied with an email explaing the above (first attempt rebuffed as too early, returned to do it at later date) but also explained that upon reflection that my personal life was a bit disrupted in September for the following reasons: a mental health scare for my daughter - which was on NHS record. And the fact that I am boat crew for the RNLI and September and August are our busiest months, with the pager going off up to 3x a day, which can be challenging. I did not provide these as excuses but as background for my distraction.
The next day they responded with the approval.
Note: I used UK Migration Lawyers. They were ridiculously overpriced for the value of what they actually do - but in a bind, without time to comb through this forum for answers, they were worth it this time. As they were able to turn it around quickly and gave me some confidence that I was doing it the right way this time around. Their service was also very good. It was nice to chat to people on the phone who seemed genuinely invested in my case- which is different than doing it on my own and hoping for the best.
Note: I studied for the Life in the UK Test by listening to a podcast which summarized the book with follow-up questions from the exam (a good starting point as it gave me the background). Then I listened to the MOST EXCELLENT series on YouTube UK Life Prep and taking free mock tests online.
I posted the above in case anyone else finds themselves in this tricky situation.
Next will be trying to get citizenship and then contemplating our next move... as I don't want to be here forever, but like the security of being able to come back if needed.