I’m not sure if this will help anyone but I figured, if time dilation track is not an option, you can change the “Play Rate” with a right click on the animation on the sequencer timeline.
It is not possible to keyframe it but a workaround is to duplicate said animation, change the play rate of both to the desired one, and then try to match them so when the sequence is played there’s a smooth transition between animations and it looks just as if you are keyframing the speed.