Swatch Internet Time might be an interesting case study: <a href="https://en.wikipedia.org/wiki/Swatch_Internet_Time" rel="nofollow">https://en.wikipedia.org/wiki/Swatch_Internet_Time</a>
No direct experience myself, but MathJS has an API for creating new units of measurement that you might consider for prototyping/experimenting/initial development:<p><a href="http://mathjs.org/docs/datatypes/units.html" rel="nofollow">http://mathjs.org/docs/datatypes/units.html</a>