Scheduling and managing events using Outlook.com calendar
While I am no script expert the way I think it works is when the script runs it goes and grabs the updated ICS and "re-syncs" if you will. So if it worked once then it would continue to work. But the variable is on the Microsoft side--that has MS updated by the ICS. That sometimes can take some time. I've read conflicting posts about how long the time period is between MS updates to the ICS and that's why I said once you are sure the script worked (i.e., the calendar is created under "My calendars") then just 24 hours.
Also check your Google drive and make sure you see the copy of the script there.