Answer to your second question is I have no idea, especially at this time of year.
For peace of mind if you can afford to send it by recorded delivery then it would be prudent to do so, as I quite often hear from claimants when things go astray, if they have proof of postage then you can show that it has been posted off whereas recorded delivery usually shows time and who signed for the item.
I would depend on how much time you have. A client contacted me today to say that he received a letter from DWP stating his claim has been closed as it was late. We managed to get it reinstated as we posted it on the 7th November and showed it was delivered on the 2nd December, post at the moment is horrendous.
Gary
Nothing on this board constitutes legal advice - always consult a professional about specific problems