The following Words spoken by the Lord Jesus Christ on the very Day He rode into Jerusalem confirm when the plague of three days of darkness occured in the Old Testament.

It's my belief that the three days of darkness occurred from the 8th to the 10th day of the 1st Month. 

It's interesting to note that the Lord had a feast in Bethany on the 9th Day of 1st Month, during which He was anointed for His burial by Mary the brother of Lazarus who He raised from the dead. The Lord then rode into Jerusalem on the 10th Day of the 1st Month and said:

“A little while longer the light is with you.Walk while you have the light, LEST DARKNESS OVERTAKE YOU; he who walks in darkness does not know where he is going. While you have the light, believe in the light, that you may become sons of light.” [John 12:35,36]

Spiritual darkness is going to overtake the minds of anyone who's not walking in the light from the 13th of April 2019 [ Day 8 Month 1]

The very atmosphere is going to be filled with a demonic presence. The only antidote is to be filled with the Holy Spirit. For all those who are not will be filled with the evil spirit of malice and wickedness!