I have worked out the same date but by a different method to you and Harold Camping, that is the 20 May 2011, but that is not the subject of this post (if you wish I‘ll share it another time).
I have been really blessed by your posts and seem to have a witness of the date accuracy, and I am also intrigued by your declaration of the first-fruits rapture along with the date you posted.
I was reading this scripture you posted and was stunned by what the Holy Spirit illuminated;
"...Christ is risen from the dead, and has become the first-fruits of those who have fallen asleep." (1Cor.15:20)
Now check this out!
Here in the UK the date is written differently as the US. The 20 May 2011 is usually written as 20:5:11. The exact reverse of the scripture reference you gave us; 11:5:20! A date hidden in plain sight perhaps?