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Most calendars allow you to set a refresh interval appropriate for your use case.
On Apple calendar Calendar right click the subscribed calendar, then Get Info → Refresh interval. And you can manually refresh by using the keyboard shortcut “command + r” (could take up to 30 seconds).
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This works very similarly on your iPhone. In Settings → Mail, Contacts, Calendars, find your Calendar Subscription and configure the Fetch Interval. Then you can even trigger a fetch manually by going to the Calendar, showing the list of all calendars, and pulling it down (loading spinner appears).
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