To integrate google calendar events into your gnome desktop, go to google calendar, click on “settings”, then on the “calendars” tab and then on your calendar’s name:
Then, at the bottom there is a section called “private address:” > click on the “ical” green icon to get your private calendar url,
Now all you have to do is open a terminal and paste this:
/usr/lib/evolution-webcal/evolution-webcal url
Replacing url with your ical private url you got in the step above.
A window will pop up and here is where you can make the update frequency settings