How to time-remap with Twixtor in Adobe Premiere? I have problem to understand, how Twixtor works. 

I want to use Twixtor plugin with my Adobe Premiere Pro. I can only change speed for whole sequence. Adobe has its own filter called "Time remapping", but that does not change speed so smoothly, as I saw in some videos.

Does Twixtor have keyframes? Where I can set start and end of slow down effect?
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: