How Many Days?

Both Matthew and Mark record Jesus discussing and giving instructions concerning His return.  He said He would return after He cuts the great tribulation short.

By how many days?

Jesus doesn't tell us.

A world leader, titled the man of sin in 2 Thessalonians 2:3, will commit what is known by Daniel and Jesus as the abomination of desolation in the temple.  (Dan. 9:27, Matt. 24:15, Mk. 13:14)  It will be a declaration that he believes himself to be God.  Many will believe this and will worship him, who will also be known as antichrist.  Those who do not worship him, he will seek to put to death.

No one knows the day or hour of Jesus return (Mt. 24:36), but it will occur sometime after we see the revealing of antichrist, when he makes his declaration, and sometime after the greatest persecution ever against believers begins.  Jesus returns and cuts the persecution against believers off, the great tribulation, and gathers the elect, at an unknown day and hour.  Jesus said if He didn't, no elect life would be saved.  (Mt. 24:22)

(The last half of Daniel's 70th Week lasts 1260 days (forty-two months), the number of days the beast is given authority...Rev. 13:5, but the great tribulation will be an unknown number but less than 1260 days...make sense?)