Passover-15 Nissan
Gen. 7:11 In the six hundredth year of Noah's life, in the second month, the seventeenth day of the month, the same day were all the fountains of the great deep broken up, and the windows of heaven were opened.
second month (Nissan) 17th day
Seven is the number of completeness and perfection (both physical and spiritual). It derives much of its meaning from being tied directly to God's creation of all things.
Number eleven is important in that it can symbolize disorder, chaos and judgment. In Genesis 11, men rebelled against God and built the tower of Babel.