Hi @Dale5 ...
Have you had an opportunity to review this Guide?
How do I subscribe to the Calendar feed using Google Calendar as a student?
I think if you take a look at the information in the light blue box at the top of that Guide, you'll find the answer you're looking for...specifically the second bullet point under the "Notes:" where it indicates:
Google Calendar periodically updates but may take up to 24 hours to sync with the Canvas Calendar. Canvas update may not be immediately visible in Google Calendar.
I hope this will be of some help to you. Let Community members know if you have any questions about this...thanks!