Name reservation starts Tuesday, 10/27
According to Blizzard, starting Tuesday, 10/27, you can reserve names for WoW Forever until 11/03 (Pacific time).
When does it start?
- Europe: Tue, 10/27, 6:00 PM (CET)
- North America: 10/27, 1:00 PM (PDT)
- Korea and Taiwan: Wed, 10/28, 7:00 AM local time
Who can do it? Everyone with an upgrade pack: Skyborne Heroic Pack, Skyborne Epic Pack or Warcraft Forever Collection.
How many? Up to 3 characters in total across all rulesets, first come, first served. Blizzard does not guarantee your preferred name.
Tip: Prepare two or three backup names beforehand. Everything about the launch: /start-checkliste/
Source
Summary by Eternadex. Blizzard's original post is authoritative.