Consider making `start-date` and `end-date` dates instead of timestamps

[iffy]

It may be granular enough to make start-date and end-date be UTC dates instead of timestamps. Consider how this will play out in different timezones and decide if it's worth it. Maybe the start-date and end-date should be the start/end date of the financial institution?

[iffy]

Re timezones. I think it might be best to include the timezone with every date, just to remove ambiguity. I'd rather that an SFIN document be self-sufficient than requiring someone to consult the standard.