Revelation 9:1 And the fifth angel sounded, and I saw a star fall from heaven unto the earth: and to him was given the key of the bottomless pit.
Revelation 20:1 And I saw an angel come down from heaven, having the key of the bottomless pit and a great chain in his hand.
IMO these verses are not parallel. One verse depicts the releasing of it's occupants, the other depicts the confining of occupants. There's also an angel to consider in both passages. And since it should be pretty apparent that these 2 passages are not describing parallel accounts, then neither can these angels be the same angel in both accounts, otherwise we have this same angel descending from heaven on 2 seperate occasions.
If we make Rev 9 parallel with Rev 20, then we have to conclude that Rev 9 transpires at the beginning of the millenium, and that satan isn't bound for 1000 yrs at all, but that he's immedietly released if the 2 passages are parallel. And if one is Amil, and sees these passages as parallel, then they would have to conclude Rev 9 occured in the 1st century. I don't know if Amils see these passages as parallel, but if they do, that's what their conclusions would add up to.