The RFC 3339 timestamp specifying the latest of the start time. If this is not set, the time of 31 days after start_at_min
is used.
Examples for January 25th, 2020 6:25:34pm Pacific Standard Time:
UTC: 2020-01-26T02:25:34Z
Pacific Standard Time with UTC offset: 2020-01-25T18:25:34-08:00