In After Effects, Time Remapping is quite logical: set a keyframe in the clip, and tell what frame should show at that time - everything in between keyframes is interpolated accordingly.
But, unfortunately, Premiere Pro messes with this principle: it kind of allows to set 'Speed' keyframes, which are not actually editable. Sure, Time Remapping can change speed, but the keyframing should be about, yes, Time. (Otherwise it should be called Speed Curve or whatever).
So please, make it possible to do Time Remapping After Effects-style: keyframes that link a source frame (time) to a destination frame (time).