[Robin Fearon] “Where is the frame blending switch and what is its relevance?”
Here’s the frame blending switch:

If you leave frame blending OFF, time remapping will not create any new frames from the source material. For example, if you’re remapping 2 frames to 4 frames, Ae will hold the first original footage frame for two frames, then the second original footage frame for two frames.
If you enabled frame blending, Ae would synthesize new frames in between the originals, giving you smoother motion (but the possibility of noticeable artifacts).
There are two frame blending modes: frame mix (which dissolves the two adjacent source frames together, with emphasis given to the frame that’s closer in time), and pixel motion (which analyzes the motion in the existing footage and attempts to interpolate that motion to the in-between frames).
[Robin Fearon] “Perhaps you could tell me, is it better to time remap footage or footage within a composition?”
It shouldn’t matter technically. I’d say do whichever is easier to keep organized in your project.
Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive | RenderBreak [blog] | Profile [LinkedIn]