How to time-remap with Twixtor in Adobe Premiere?
Just like with any effect property you can animate it by clicking on the little stop watch on the left of the effect property name (see below).

You can apply the effect to just a single clip, you don't have to use it on the entire sequence, just drag and drop the effect from the effect list onto the desired clip and then animate the speed of the video via keyframes.

A screenshot from the "Effects Control" panel: