Capitalisation implies that the name has been elevated to have meaning in its own right, not just as a literal description. For example, if the mezzanine between the 1st and what was the 2nd floor was converted to be the 2nd floor, what had been the 4th floor would become the 5th floor but might be referred to as "the 4th Floor". Similarly, say a company owned two bookstores, and in the ...
"on the 5th of November" is practically just removing the word day from the reference. As in "on the 5th (day) of November." It is used everywhere and even though it could be understood a few different ways it is the most correct. "on the 5th November" seems to me to more be dependent on the month and if not year. As in "it's my baby's 5th November" as in, the child is experiencing November ...
grammar - When referring to dates, which form is correct? "on the 5th ...
"5th May" would be the most traditional way to write this date. I have never seen "of" used in a written date, except in extremely archaic constructions such as legal contracts "signed and witnessed this 5th day of May 2012" (Parenthetically, I note that in English law this makes absolutely no difference to validity.
Saying "till" doesn't make it clear if you're returning the morning of the 5th, or if the 5th is included in your leave. To be absolutely clear, you should state when you leave and when you return. I will be on leave October 4th and 5th, and I will return October 6th. This makes it clear which days you will not be in the office.