"Question for the learned folk is how and when are the confidentiality of the wells lifted and announcements made"
As soon as they've tied up what leases they want around the well is the usual reason.
as for time, it's 6 months up in ND - our Bakken acreage
you can find the confidential well list here:
https://www.dmr.nd.gov/oilgas/confidential.asp
(well info date release, far right column)