Teamfight Tactics' official release this week will be staggered based on region in order to avoid heavy load on Riot Games' servers, according to this post on the League of Legends forums from a Riot communications specialist.
If you've attempted to get into the closed beta since its release to the PBE, only to be met with a seemingly infinite loop of login queues, might be happy to see Riot taking these precautions. Although the live servers are much larger than the PBE's, they want to do whatever they can to ensure the open beta launches smoothly. Here is how TFT will roll out over the course of the week (all times are PDT).
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*A level requirement of 10 or higher will be implemented in these regions temporarily.
For NA, EU, KR, VN, TW, LAN and LAS, all missions related to TFT will be disabled until a week after the mode's release in those regions and will become available everywhere once Riot is sure that things are running as they should be. On top of this, they'll be disabling server transfers, practice tool, and customs of less than 10 people in all regions.
This is the first time that Riot has placed server restrictions of this scale in preparation for a release of any kind. While these changes will affect a wide variety of the player base in many ways, it's important to note that they will only be in effect until Riot is confident that the servers can handle the influx of players. At least it beats waiting 15 hours to log into the client at all.
To prepare for the game's release, take a look at the official trailer and mini-site for TFT.