Times for data

[jordan-evens]

I think we're all good with using the different libraries based on https://github.com/evansiroky/timezone-boundary-builder/ for timezone handling, so we can avoid worrying about that and just use Zulu.

It sounds like we're good with using start/end/interval for defining data times, so if Erick finds the spec he was referring to I can try to pull the relevant pieces into our schema.