It is difficult to know for sure but we know from Rev 19:20 both of them are around until the Second Coming and I imagine both of them will be very busy while they have the chance.
Rev 9:11 And they had a king over them, which is the angel of the bottomless pit, whose name in the Hebrew tongue is Abaddon, but in the Greek tongue hath his name Apollyon.
Rev 11:7 And when they shall have finished their testimony, the beast that ascendeth out of the bottomless pit shall make war against them, and shall overcome them, and kill them.
These scriptures seem to indicate to me that the beast who kills the 2 witnesses can't be around at the start of the 70th week to confirm a conevant as he only seems to show up just before the Mid-Point events when the bottomless pit is opened at the 5th trumpet/1st woe, taking the book of revelation chronologically.
Maybe it's possible this means a new level possession of the Anti-Christ figure takes place at this point as part of this revealing but it seems to be more literal than that to me?