Outlook ics calendar not updating
For more information about Internet Calendars, see the link in the See Also section.
I think I see the issue and it's due to the fact that Google Calendar appears to update its ical sources only every 24 hours.
There have been requests to either update it a bit more frequently or provide users with a manual refresh option - see link below:
Internet Calendars are calendars that are shared through the Internet.
These calendars are based upon a global Internet standard that allows calendar information to be exchanged between people regardless of the application that is used to create or view the information.