4:00 -18 from the watch?? What is the significance of 400?

The number 400, which is arrived at by multiplying 8 by 50, symbolizes in the Bible a divine perfect time period.

A 400 year period exists from God's fulfilling of his pledge to Abraham in Isaac's birth to the children of Israel leaving Egyptian bondage. Stephen, in his testimony before religious leaders just before his martyrdom, mentions the starting point of this count (Acts 7:6), which agrees to what the Eternal stated in Genesis 15:12 - 13.

This is what God said to him (Abraham, the father of the faithful): 'Your descendants will live in a foreign country, where they will be slaves and will be badly treated for four hundred years (Acts 7:6).

Slaves no more