Via the GNOME Wiki, the release schedule was for GNOME 3.22 was ratified earlier in the week. The date most people care about for GNOME 3.22 is 22 September, the planned release date of GNOME 3.22.0. Though, of course, it's no big surprise considering the release usually lands right around that time considering their release cadence.
GNOME 3.21.1 as the first development release is planned already for 27 April while those snapshots will continue until the GNOME 3.20 Beta on 17 August followed by a second beta and the release candidate. GNOME 3.22 is codenamed "Karlsruhe" due to the recent decision by GNOME to begin using codenames and deriving the names off the locations of their conferences, with this summer's GUADEC conference happening in Germany.