I think it must be asked what is he bound from doing.? Assembling with the angels that have not left their first place estate?
Job 1:6 Now there was a day when the sons of God came to present themselves before the LORD, and Satan came also among them.
He is not bound so much that he cannot accuse the brethren day and night . If he is bound rendering him useless then who is it that as accuses us, when God forgives us.
Revelation 12:10 And I heard a loud voice saying in heaven, Now is come salvation, and strength, and the kingdom of our God, and the power of his Christ: for the accuser of our brethren is cast down, which accused them before our God day and night.
What does it mean to be reserved in everlasting chains unto the judgement day the last day. Can a literal chain hold a lying spirit that has no form.
Jud 1:6 And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day.