The worst part of any MMO launch is getting stuck in a hours-long login queue. When World of Warcraft Classic released a few years ago, some players were stuck in lines up to 30,000 players long. The new Shadowlands expansion probably won't be as bad, but you can avoid the pain altogether by logging in right now, skipping the inevitable rush when Shadowlands goes live at 3pm PT/11pm GMT.
Unlike previous expansion launches, World of Warcraft won't be going offline temporarily to roll out Shadowlands. Instead, at 3pm, all players will receive a new quest beckoning them to return to Stormwind or Orgrimmar so they can begin Shadowlands' story campaign. A lot of players will still undoubtedly wait until 3pm before logging in, however, so if you're on a more populated server it's very likely you'll get stuck waiting in line. Unless you're smart and log in hours earlier to prepare.
Blizzard explained all of this in a new blog post setting expectations for Shadowlands' launch, including some useful information about when certain features associated with the Battle for Azeroth expansion will go offline. For example, bosses and quests associated with the current pre-expansion event will shut down an hour before at 2pm, and players should be sure to loot their weekly chest from BFA's Mythic+ dungeons right now as there won't be another one.
With regards to the login queues, though, Blizzard didn't give much specifics other than explaining servers won't be going offline. It's better to be safe than sorry, though, so if you do plan on jumping in right away I'd recommend logging in at least two hours before—possibly even earlier depending on the size of your server.
If you don't know how to check your server population, you can login to the game now to get to the character select screen. From there, select choose realm and you'll see a list of all the available servers with their current population listed on the right. Keep in mind that's a reflection of their active population, however, so just because your server might be at low doesn't mean it won't reach full when Shadowlands launches in a few hours.
For more tips on how to prepare for Shadowlands' launch, check out our guide.