These dates have changed AGAIN as of March 30, 2025 March 16, 2025.
Ok, so it's ridiculous that for such a huge change, I had to search Google to find a Reddit post that referred me to this YouTube of a webinar hosted by the Boise Atlassian Community (shout out to @Erica Larson) that FINALLY had a list of rollout dates (as of Feb 14, 2025, YMMV, T&C MAY APPLY, READ THE FINE PRINT, SUBJECT TO THE WHIMS OF ATLASSIAN PMs, ETC ETC.):

For better Google indexing, I'll type it out:
Rollout Nav Timeline (Directional)
(Products: Jira, Jira Service Management, Jira Product Management, Confluence, Atlassian Home, Focus)
Today (Feb 14, 2025)
- EAP and Open Beta Customers
March '25
- Start rollout for Standard edition
- All Free Edition
- All new Trials
- Opt in for all Sandboxes
July '25
- Start rollout for Premium edition customers
September '25
- Start rollout for Enterprise edition
December '25
- 100% all customers on new navigation