Well basically, it because the calendar service you're using hasn't got the latest and greatest information from teamstuff. The way these services work is that they will regularly go out to the calendar source ( teamstuff ) and pull back the schedule. But how often is regular? Every service has its own time frames, but its unlikely to be quite as fast as you'd like. Hence you might see an issue.
Google keeps a cached copy of the calendar ; and it refreshes that copy every 24hours or so. We don't really know how often, but it's something in that order. You can't manually refresh external calendars in google either, so you either need to wait for google ( prob less than 24 hours ), or force google to get the contents from teamstuff right now.
This is what you need to do;
1. Remove the calendar from google
2. Re-add it using the teamstuff calendar URL , but this time add a ?1 after the .ics. ( The ?1 is a way of passing parameters in URLs - the parameter is ignored by teamstuff but its enough to ensure google will not use the google local copy of your calendar ).
3. Google will then go out to teamstuff and get the latest and greatest calendar - and it will be up to the minute.
The technique is sound for other calendar applications too; the principles are the same for all calendars.