I believe when a saint enters the perpetual rest, he has reached the end of time and entered eternity. For him, there is no more time since he has heard the Seventh Trump and the mystery of God is finished for him. Time goes on for others however.
So did John hear it? I say he did and he wrote in Revelation about hearing that voice like a trumpet. He also wrote about being "caught up." Did he see the return of Jesus before he died?
There is an interesting story about Peter asking Jesus about John.
John 21:21 Peter seeing him saith to Jesus, Lord, and what shall this man do?
22 Jesus saith unto him, If I will that he tarry till I come, what is that to thee? follow thou me.
23 Then went this saying abroad among the brethren, that that disciple should not die: yet Jesus said not unto him, He shall not die; but, If I will that he tarry till I come, what is that to thee?
Did John achieve a state of sinlessness? I think he did. It may be rare in this world, but I think he did.
Hebrews 9:28 So Christ was once offered to bear the sins of many; and unto them that look for him shall he appear the second time without sin unto salvation.