There isn't much to how it's decided when packages such as PCSX2 are updated to newest version.
For example for PCSX2 that decision is based on how many changes have happened since current version in repository and if there have been important fixes or nice to have features added. If there are new important fixes or nice to have features added then the package could get updated even just days since last update.
For all packages in the Xservers debian repository when to update them is done same way as for PCSX2 in example above.