Google-calendar – How to enable popups in Google Calendar when tab is closed

Google says every few hours, which in my experience means 6-24.

Currently, calendar feeds are automatically updated by Google Calendar every few hours. We understand that some users want to have the ability to refresh the calendars they added manually and we are exploring various ways to enable this.

If the calendar you're subscribing to using Google Calendar isn't refreshed after 24 hours, please send us the calendar address and the detail of the problem so that we can investigate.

Source

Not with the native interface. It looks like all of the data is already in the page and it's using JavaScript to change what is being displayed on the screen; it isn't opening a new page at all. It's not a classic link, so you can't right-click and choose different actions, for instance.