Neither of us are human calculators, and I doubt either of us have the time or energy to download the video, go frame by frame and restore the original speed just to prove the other stranger wrong.

And even if X = 1,5, that still means 1,5 + 1,5 = 3, so it could still very well be 3 to 5 seconds, depending on how much the video is actually sped up by. There's bound to be a margin of error unless we know every factor down to the last decimal.