現在行われております、Ship01～Ship05の新規キャラクター作成の制限は接続人数の状況を見て解除いたしますが、今夜中のキャラクター作成制限の開放はございません。大変申し訳ございませんがご了承ください。 #PSO2
— PhantasyStarOnline2 (@sega_pso2) June 21, 2012
Sorry for the long delay but Ricardo can't stay up 24 hours. Based on the official Sega twitter feed, there may be times when you can not make a character on certain due to overcrowding. Around peak times, the server may get congested and you'll be locked out of the character creation process for that ship.
Ship Congestion Error Message
The error message will inform you to create a character on another ship. Currently the English community has not decided upon an alternative ship, but current suggestions seem geared towards Ship 7 through 9. Unfortunately you can only create one character per account due to Arks Cash services not implemented in the Open Beta test.
If you want to play on another ship, you must delete your first character, then remake them on a different ship.