Notice over frame 390 is a new icon. Whenever you want to retime an animation to go faster or slower all you have to do is select the icon after you highlight anything in green (except audio) then with the middle mouse button pressed you can expand or collapse in scale.



1) Select all keys you want to rescale in time.
2) Position the framehead to determine the beginning of the animation collapse or stretch.
3) Then hit the rescale icon.
4) Middle mouse drag towards the framehead to scale speed up or away form the framehead to scale slow down.

In this example below the animation is sped up from how it was initially as dragging left pushes in scale the keys towards the framehead.
Unlike normal dragging this action drags keys slower when closer to the framehead and faster the further away they are.