Checking Naturalisation Eligibility Date

Hello all,

Sorry for creating a post for such a small question--it seriously feels so stupid--but I'm hoping someone can confirm this for me. 

I went from 5 year WP to ILR last December, so am coming up to my eligibility for naturalisation in a few months.  What I'm trying to confirm is when my year mark is.  My letter from the Home Office confirming my ILR success (I'd had an in-person appointment on 16 Dec but my employer screwed up my letter; oh you should have seen my crying outside the office. My mom had also died that year and my employer was hounding me about that too, so I was a little sensitive) is dated 18 December.  But my BRP says 'valid until 18-12-2023' and 'place and date of issue 23-12-2013.'

So am I able to go with 18 December for my year point--and thus making myself an NCS appointment from the 19th ( )--or do I need to wait until 23 December?

(Bonus question, does anyone have experience of submitting their applications close to the Christmas period?  Am I running the risk of the Home Office not opening my packet until January, and thus checking my 'were you in the country 5 years ago' on a random January date?)

It's the 18th (thinking because the biometric cards are send out seperately that's why the date is what it is)

I received my ILR on the 14th December 2012  (I'm sure I received my original Work Permit Visa on the 18th December, which made me smile when you wrote it.)
  Anyways, I was eligible 14th December 2013 for Citizenship ,but I waited until January 8th for my NCS appointment, as I counted back through my dates out of country and I knew that I was, for certain in the country and for a good few weeks (to allow for them any delay in processing my application). 

Not long now, you're almost there!! 

Thanks, phatbeetle!  It's soooooo close!