Yeah it looks nicely simple & modular, but it probably works best in Node.js since your servers can all be in UTC.
In general I see the appeal of using a small shim around a standard library thing rather than re-implementing something totally new, but JS Date is bad enough that you're better off staying away altogether. It's just hard to use correctly since there's no "timezone unaware" object available and it always assumes the local timezone, so users' browsers in different timezones treat them differently. Lots of seemingly simple things (e.g. a time + timezone input picker) are easy to mess up because you end up accidentally implicitly converting things to the local time.
In general I see the appeal of using a small shim around a standard library thing rather than re-implementing something totally new, but JS Date is bad enough that you're better off staying away altogether. It's just hard to use correctly since there's no "timezone unaware" object available and it always assumes the local timezone, so users' browsers in different timezones treat them differently. Lots of seemingly simple things (e.g. a time + timezone input picker) are easy to mess up because you end up accidentally implicitly converting things to the local time.