While there is no fixed limit on how many characters of each Type there can be on the game, the Admin have established a quota for how many characters of the higher Tiers (III, II and I) that there can be. The quotas are a percentage of the number of PCs (this includes unapproved characters) that exist on the game, and players can check if there are any slots open for a specific tier by using the +cdb/quota command.
However, a slot is not considered to be available unless it as also been announced on the in-game Notices board and on the Announcements blog. Whenever a new slot opens up, an announcement will be posted, and for a specified period following the announcement all who request will get a chance to apply for the slot. If the slot is not filled during this period, it will remain open and can be requested and applied for on first come, first serve basis.
Unless the announcement specifies otherwise, from the date of the announcement players will have 3 days to put in their requests for characters of the tier that has been made available. Players who place their requests within the 3 days will have the application sent to them at the end of those 3 days. Requests made after the 3 days will be denied unless less requests than the number of open slots were received.
Players who requested within the time limit will then have 7 days to send in their application. Once the 7 days have passed, the Admin will look over all the applications to determine which, if any, will be approved.