At Timetastic we see occasional requests from customers experiencing problems with Google Calendar, usually Google calendar stops updating changes to their Timetastic calendar.
Unfortunately resolution of this issue tends to be a waiting game 🙁
By way of some background, the way an iCal feed works is that it is your calendar application (Google in this case) which periodically requests an update of the information from Timetastic i.e. Timetastic does not push the data to you calendar, it's your calendar that requests it from Timetastic.
Although Google updates the calendar automatically from the Timetastic feed the timescales for this are somewhat unclear and there is no manual way to force the update.
Some observers have suggested Google updates every few hours, but Google themselves quote it may take up to 12 hours, although in in exceptional cases we have seen it take as long as 48 hours.
To help with this, we now report iCal feed hits back to Timetastic for all users. This means you know when your calendar app last checked in and as a result, whether it's up to date.
In your calendar feeds page you'll see the latest fetch time when hovering on the clock (and if we can identify it, the service that checked in).
Seeing orange icons there means it's been more than 24 hours since the last poll, so your calendar app is having issues contacting us.
As the amount of data we gather from this grows, we're hoping to improve our iCal update rate. We're building up a data set using all of our iCal hit data so hopefully we can start to identify trends and issues that crop up.
Some clients have reported success by deleting the feed from your calendar completely and reinstalling it, it seems that in some instances this is sufficient to kick start the updates again.
Note: Since first writing this article back in May 2015 Google have altered their timeframe for update from 8 hours to 12 hours - which seems to indicate it's an ongoing problem and they are not taking steps to improve the situation.
And finally, sometimes you can take comfort that you're not alone - here's a thread on Google's forums that's been running since 2013 of people complaining about feeds not updating Google Calendar not updating published calendar added by URL