If someone gets saved in those three seconds, they probably would qualify as Tribulation saints. However, I doubt there will be many who accept Christ in that 3 second time period.
I do not know if that is possible anymore. When we say we believe in the rapture what we are actually saying is:
WE BELIVE IN GOD'S GRACE AND PROMISES THROUGH THE LORD JESUS CHRIST!
After the age of grace ends with the rapture all bets are off. God's focus is then on Israel again:
Ephesians 2:12 ... remember that at that time you were separate from Christ, excluded from citizenship in Israel and foreigners to the covenants of the promise, without hope and without God in the world.