Some users experience problems with updates to the ShowHouse calendar taking a long time to reflect in their Google calendar when they have subscribed to it.
Unfortunately there is no immediate resolution of this issue. From a technical point of view, the way an iCal calendar feed works is that it is your calendar application (e.g. Google Mail or Microsoft Outlook) periodically requests a data update of the information from ShowHouse. Our calendar does not does not push the data to your Gmail or Outlook (it is pulled from their end), so we don't have any control over that update schedule, and there is no way to manually force this update.
The update schedule itself is unclear. It has been our experience that this is typically every few hours, but Google themselves quote it may take up to 12 hours, and in exceptional cases we have seen it take as long as 48 hours.
Although it may not be any consolation or provide any resolution, this Google forum thread has been running for over 2 years of people complaining about feeds not updating Google Calendar not updating published calendar added by URL.
As and when we find out any more on this issue, we will let you know.