A.T. Robertson Commentary Revelation 20:7

"And when the thousand years are finished, Satan shall be loosed out of his prison," — Revelation 20:7 (ASV)

When are finished (οταν τελεσθη). Indefinite future temporal clause with οταν and the first aorist passive subjunctive of τελεω, "whenever are finished."

Shall be loosed (λυθησετα). Future passive of λυω, no longer bound as in 20:2f. He uses the future as a prophet in verses 7,8, but in 9,10 he uses the aorist as a seer.

Out of his prison (εκ της φυλακης αυτου). For φυλακη in this sense see 2:10. Out of the abyss of verses 2,3.