This is not about predictability of the timeline. The way it works is that it calculates, based purely on the delta time from the current frame versus the previous, where in the timeline curve you are and outputs that value accordingly. So you should never use the raw output to change the position of anything, as you cannot predict or control the frame rate.
For example, if your timeline is a simple line set as 1 for every output, and your frame rate is 30 the offsite will be 60 per second if you are running at 60 frames per second, or 30 if you are running at 30 frames per second. Using it that way is just wrong.
Instead, set the timeline as the position that your actor should be, and set the actor to that position each frame instead of adding a delta. That will ensure that by the time X in your timeline, your actor will be precisely in position Y. That makes sense?