Google calendar timeline will get the data from your calendar and display it on a separate timeline. Data is NOT saved locally, so you need to be online to get the data.
To add Google calendar timeline, open Timeline editor, then click Add timeline button, choose Google calendar and click Next.
Next you will be transferred to google where you need to authorize ManicTime to view your calendars.
Then go back to ManicTime and choose which calendars you would like to see.