It helps to look at Matthew 24 Mark 13 and Luke 21 side by side. Luke writing for his Gentile friend Theophilus put Jewish language into a form understood by Gentiles.
(e) The Destruction of Jerusalem (Mt 24:15-22; Mk 13:14-20; Lk 21:20-24) [Note Luke 21:22 – “To fulfill all that is written”] Flee when armies surround Jerusalem to be instruments of God’s judgement: the end is not coincident with Jerusalem’s overthrow.
Christ’s return will not be on earth to be seen by a few but in the heavens to be seen by all.
Occurs immediately ‘after the tribulation of those days’ (Mt) ie the inter-advent period, and men are powerless before Christ’s glory.
To watch is not to know dates but to live in a godly way. Christ’s return comes in a time unexpected, in the midst of normality, and after what seems like delay.