drew the sketch, took a frame, removed a bit, took a frame...

Yes exactly ...and erm not....
sketched the whole sketch on the first page(first frame)...

Copied duplicates several times of the same as first sketch page eg. 15 frames (of first frame sketch)
then working back up the frames from the bottom...altered each frame...removing a bit, changing a bit, adding a bit, as I worked back up to the original sketch.

[tilts head to oneside] after rereading my working its possible I have a dislexic approach?and faster, which I believe was your goal to begin with]
because trying to do it after first frame working down through frames adding line by line one each phase of the drawing sketch on each frame was more difficult for me

::: either way, the principle is still the same with copy/duplicate all frames then edit each frame

have I complicated a simple process in explanation...lol

so here's an equation
frame 1 = first frame sketch = a fast freehand simple line drawn image
frame 2 = duplicate frame 1 =first frame sketch
frame 3 = duplicate frame 2 =first frame sketch
etc...

...was this helpful?

ps. Yes time of animation can be altered with 0.1 of second to long drawn (lol pardon the pun) seconds whatever you wish...