Sounds lovely, would be great if it worked on my old watch.
It requires watch os 9. Check this first in your Watch app, General, About. If you have e.g. v8.8.1, don’t bother, won’t work. Best of luck, I may try again when this watch dies and I get a new one. Installed twice, once with setting “automatically as watch companion apps”. When looking at the Apple Watch app, pocket watch is not listed. Maybe there it’s a requirement of a specific version of Apple Watch, who knows? Nothing mentioned in the forum or in the instructions.