Bangle.js time steadiness

I think that's probably about what you'd expect. Most crystal oscillators are rated at around 20ppm (parts per million). From Wikipedia:

Typical crystal RTC accuracy specifications are from ±100 to ±20 parts per million (8.6 to 1.7 seconds per day), but temperature-compensated RTC ICs are available accurate to less than 5 parts per million

In a day you have 60*60*24 = 86400 seconds. So to keep accurate to within 1 second you need a 12ppm crystal. If you're seeing 2 seconds then I guess that's about what you might expect from a 20ppm crystal.

Even with a separate temperature-compensated RTC you'd still be looking at drifting by maybe 0.5 sec a day.