Their white garments, and golden crowns seem to indicate that these 24 represent the redeemed.
The question is which redeemed? Not Israel because they aren’t saved until near the end. Not the unsaved because that happens after the 7 year tribulation.
Call it Anything but Boring Revelation 4:1-11NKJ
After these things I looked, and behold, a door standing open in heaven. And the first voice which I heard was like a trumpet speaking with me, saying, “Come up here, and I will show you things which must take place after this.”