Many functions on the Savannah web site affect accounts on other GNU machines. This includes all functions related to mail aliases, shell passwords, user additions, group member changes, CVS repository creation, etc.
Updates to these and other systems happen via cron every 30 minutes, so changes made on the web site will appear to be live, but will not take effect until the next cron update.
ViewCVS never recomputes the \~2500 projects list (it would consume too much resources and time to do it at each request) - but Apache2 (hence ViewCVS) is restarted daily by sysklogd. So as an exception, new projects are taken into account by ViewCVS only every 24h.