There is a server limit for AdventureQuest as the server can only hold so many players until it overloads and crashes, thereby going offline. This limits the number of non-paying players who can play the game at once. One of the perks for being a Guardian is the ability to access the game whenever one so wishes to do so, regardless of the server limit (except for when the server is offline).
New accounts (regardless of Guardian/Adventurer status), can bypass the server limit and in effect login anytime they wish for 6 times. This is to allow them to get a feel of the game before making a decision as to whether to obtain Guardianship.
As of June of 2011, the server cap was removed.
The server limit depends on the number of players online and the server stress. For example, when the server limit is 6300 and there are 6257 Adventurers online, 43 more Adventurers and Guardians can login until the server limit is breached.
Once the server limit is reached (6300 Adventurers online), only Guardians will be able to login until a sufficient amount of players logout for the number of players online to go below the server limit again.