What does "speed" mean in effects?

[Thysbelon]

I'm trying to do a note slide with effect E1 (I could probably also use 03 as an alternative), but I can't set the duration I want because I can't figure out what "speed" means.
Ideally, in the DAWs I use, I want to be able to set a note slide by inputting the final destination note, and the duration of the slide (how long it takes to get to that final note);
Furnace Tracker doesn't have an option to set the duration of a note slide, it only has a "speed" option. If I knew what "speed" meant, I could calculate the speed value needed to get the duration I want; but I can't find any information on what "speed" means for effect 03 or effect E1/E2, only vague descriptions like "1 is slow and F is fast".

The discussion most similar to mine is "Improve Effect listing for new comers.", but I couldn't find the answer to my question there.

edit: I did more testing using the Game Boy chip. The relationship between the speed setting of E1 and duration of the slide is not a straight line.

1 speed is 111 milliseconds per semitone
2 speed is 43 ms per semitone.
3 speed is 29 ms per semitone
4 speed is 17 ms
5 speed is 16 ms

(none of these numbers are exact.)

edit: If I never find the exact numbers, I'll settle for using Audacity with WASAPI, loopback, and spectrogram to check if my note slides are close enough.