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There is actually a (paid) app that does specifically this for Android! It's called Watchface Scheduler for Pebble, and after importing all your watchfaces, it lets you set up different schedules for setting specific, or random faces at certain times a day, on certain days (Or every day).
I have mine set up so every night it changes to NIGHTFACE every night, and then to choose a random watchface at certain times a day.
I've had good luck with Watchface Scheduler in the past. Before that, I also used Catapult in conjunction with Tasker, but seeing as that's been a long time since it's been updated, I'd go for the former.
Do you mean change to a different watchface? If you use an Android phone, you can do this with Watchface Scheduler ($1.10).
If you use Android, then look at Pebble Watchface Scheduler (US$1.10). The developer is keeping it up to date. (I have not tried this app myself.)
I use NightFace along with Watchface Scheduler for Pebble to automatically set it as my watchface at 11:30 PM.
This works pretty well for changing watchfaces but the UI is pretty confusing (don't know if the watch face tab or the schedule tab takes precedence)
https://play.google.com/store/apps/details?id=au.com.wallaceit.pebblewatchfacescheduler
Pixel Grid Digital, Neon 80s, Rotomotion Black, and Simple Striped are some of my favourite 'less popular' watch faces. I also use Watchface Scheduler for Android to pick a random watchface several times a day, which I find great. It does cost around $1, but I think it's well worth the price.
If you have an Android phone you may like to try my app Pebble Watchface Scheduler:
https://play.google.com/store/apps/details?id=au.com.wallaceit.pebblewatchfacescheduler
https://play.google.com/store/apps/details?id=au.com.wallaceit.pebblewatchfacescheduler
I have it set to randomly rotate each hour so I can go through all the watchfaces I enjoy
On Android there's Pebble Watchface Scheduler.
https://play.google.com/store/apps/details?id=au.com.wallaceit.pebblewatchfacescheduler
Android only, but otherwise looks good: https://play.google.com/store/apps/details?id=au.com.wallaceit.pebblewatchfacescheduler
There is also the (paid) Android App Watchface Scheduler for Pebble
If you're an android user you can already schedule your watch faces with this app: https://play.google.com/store/apps/details?id=au.com.wallaceit.pebblewatchfacescheduler
Watchface scheduler. https://play.google.com/store/apps/details?id=au.com.wallaceit.pebblewatchfacescheduler it costs like $1 (can't remember) but it's 100% worth it. I use it every day.
As an Android user, you can do this via the app Watchface Scheduler ($1.10).
I've just released just that for Android: https://play.google.com/store/apps/details?id=au.com.wallaceit.pebblewatchfacescheduler