I think that code will just get stuck at -1 and 24. This should work a bit better (untested):
min: -24,
max: 23,
step: 1,
format: v => (v+24)%24,
onchange: v => { /* same as above */ }
As for why you aren't seeing your changes - a bit of a long shot, but you could be running into this issue. If that's the case, upgrading to a newer firmware version should help.
Also, I assume you're using the espruino IDE to upload your changes to the watch? You might find it more convenient to clone the repository locally and test your changes using either apploader.js or a local server, as discussed in this thread.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
I think that code will just get stuck at -1 and 24. This should work a bit better (untested):
As for why you aren't seeing your changes - a bit of a long shot, but you could be running into this issue. If that's the case, upgrading to a newer firmware version should help.
Also, I assume you're using the espruino IDE to upload your changes to the watch? You might find it more convenient to clone the repository locally and test your changes using either apploader.js or a local server, as discussed in this thread.