When `millis_since` becomes larger than one week, `delay` becomes
negative and is set to Zero. This causes an infinite loop and therefore
100% CPU usage (single thread).
// FREEBIE
Display format consistent with Android:
* relative time for everything from today
* Day of week + time for within the past 7 days
* Static Month Day time for everything older
Each timestamp will only update as often as needed to stay accurate,
which is once a minute, once an hour, once a week, or never.
// FREEBIE
