This information is not publicly available anywhere besides the normal settings page. And even then it is largely unreliable since worlds are created in the backend weeks before the world actually starts and the community manager decides 5-7 days in advance the actual date (and configures it as such), but can still adjust this up until 30 minutes before start.
This would mean you would display inaccurate data up until that point. Exactly because of this reason we are not providing any of these timestamps (besides the settings page) until the world was announced (and manually configured).