Post-Tribbers like to insist that Revelation 20 tells us when the First Resurrection happens. It does not, it refers to these Saints as already Resurrected.
Resurrection happens at the Seventh Trumpet, and we see Resurrected
Church Believers in the Heavenly Zion in chapter 14, and Resurrected
victims of The Image of The Beast in chapter 15. It is the saints seen
in Chapter 15 who are most directly defined as those being refereed to
in Chapter 20 as reigning with Christ during The Millennium.
But I should also point out that the
term "first resurrection" is a classification more so then a sequence. Like Amalek being called the First of the Nations in Numbers 24:20, when as a bastard of Esau he was no where near the first to come into existence. Or saying something is First Class.
begins with Jesus, then those Matthew 27:51-53 refers to as rising soon after
Jesus did. Then The Church at The Rapture, and then those incorrectly
called by pre-tribbers 'Tribulation Saints" right after they are Martyred. This goes back to my many
other posts on The Resurrection.