The 144000 Jews from the 12 tribes of Israel are sealed before the tribulation starts

Revelation 7:1-4

After this I saw four angels standing at the four corners of the earth, holding back the four winds of the earth to prevent any wind from blowing on the land or on the sea or on any tree.   Then I saw another angel coming up from the east, having the seal of the living God. He called out in a loud voice to the four angels who had been given power to harm the land and the sea: “Do not harm the land or the sea or the trees until we put a seal on the foreheads of the servants of our God.”  Then I heard the number of those who were sealed: 144,000 from all the tribes of Israel.

The sealing of the 144000 is mentioned in the interlude between the opening of the six and the seventh seal.   The four angels are instructed not to harm the land or the sea or the trees until a seal was put on the servants of God.

The 144000 are most like the Woman in Revelation 12 that is pursued by the dragon for 1260 days or times time and half a time.  The Woman is taken to a place in the wilderness where she is protected for the duration of the Great Tribulation.  It, therefore, follows that the 144000 must have been sealed before the Great Tribulation starts.

As with the Gentiles who trampled the Holy City for 42 months and the two witnesses who prophesied for 1260 days, the 144000 are sealed and protected for 1260 days.  The point at which these events are mentioned is at their conclusion after 1260 days corresponding to the interludes between the 6th and the 7th trumpet or the 6th and the 7th seals.

 

http://truthinlove.com/References/seven_seals_trumpets_bowls.htm

http://www.truthinlove.com/analogies/seven_seals.htm

http://www.truthinlove.com/References/last_trumpet.htm