quicksilver punched apocalypse 7 times before he got trapped.
Quicksilver pretty much traveled 10 - 15 m for each punch.
So he traveled 7 x 15 = 105 m.
According to Google "The average reaction time for humans is 0.25 seconds to a visual stimulus, 0.17 for an audio stimulus, and 0.15 seconds for a touch stimulus."
Apocalypse should have at least took 0.15 sec to realize that he got hit and then he reacted to quicksilver's movement.
Speed = distance / time.
= 105 / 0.15 = 700 m/s = mach 2.05.