The 40 is an amplified 4.  The flood rained 40 days/nights.  The days of Joseph's embalming was fulfilled 40 days.  Moses life was divided into 3 sets of 40 years.  The spies of Moses scouted out the promised land 40 days and when they returned with a negative report, God cursed them (all age 20 and over) to wander to their death each day for a year in the desert....a total of 40 years.  Moses was on the mountain to meet God (and fasted) for 40 days and did this twice.  At exactly 40 years, Joshua led them over Jordan to the promised land at the time of the Passover in the month of Abib.  Several judges ruled over the Israelites 40 years.  Saul, David and Solomon all reigned 40 years.  Goliath defied Saul and the army of Israel 40 days.  Ninevah (in the story of Jonah) was on probation 40 days.  Elijah was on the mountain to meet God (and fasted) 40 days.  Jesus was tested by Satan (and fasted) in the wilderness 40 days.  Jesus walked on the earth after His resurrection 40 days.  Jesus ascended to heaven with many resurrected saints on the 40th day.
I'm sure I missed a few.

The most remarkable thing:  You never see where a period of 40 is shortened or lengthend.   It is considered to be a period of generational testing.  It generally fits between the person's ages of 20 and 60.  This was the ages that a levy (tax) (offering) was the highest and the ages in which you as a male were subject to be called to war.  Modern Israel (Judah) was 19 years old in June 1967 (born in May 48).
If the resurrection of the dead and rapture of the living occur at the 40 year mark from this sign found in Mat 24, Mk 13 and Lk 21, then Judah (State of Israel) will be 59+.  If Jesus returns in the fall at the Jubile mark of 50, then Judah (State of Israel) will be 69+, just shy of the 70 years that Psalm 90:10 tells us is the normal days of a man.

Steve