This Google Calendar™ add-on '123 Time registration' will sync your Google Calendar™ data towards your Google Spreadsheet™. Within the spreadsheet you can easily analyse your spend hours and categorize your hours. 

 * Track your personal productivity during the day by analysing how you spend your time.
 * Prepare time sheets for your clients with clear descriptions of the tasks.
 * Capture per project the time assigned to certain tasks.

How it works
From the Google Calendar™ sidebar, click first on the 3-dot navigation menu to create a Google Spreadsheet™ to keep track of your hours. 

[1] Select which secondary calendar you want to sync. No Calendar visible? First create a secundar calendar.

[2] Provide the sync options. You can decide to overwrite the calendar event title and/or description.

[3] Start the calendar sync from the start date towards today.

View the result in the Google Spreadsheet™ you created by clicking the 'Spreadsheet' button. After the first sync, you can open the spreadsheet file and you can:
 * View the synced calendar items. 
 * Use the 3 categories to assign your time. 
 * Use a formula or type a new title or description for the Calendar event. This information can sync back to the Calendar event during the next sync.

More information available in the help guide (copy/paste URL):
https://docs.google.com/document/d/1BHQ_ONjxYTF2G6s4RhJG_UqbTo1wF03gP59jBjEGhiY/preview