Flexibits, makers of popular calendar replacement app Fantastical 2 for iOS and Mac has released an update to its Mac app. The update adds near-instant Google calendar updates, instead of merely refreshing the calendar at a set time interval as has been the case in previous versions.
Flexibits notes in a blog post the feature is launching in beta form so the developers can monitor the required push server and ensure everything works as expected. That said, you may still encounter bugs or hiccups.
Also noted in the post is that Flexibits has no access to any of your personal information, the push server simply relays information from Google to the app that something has changed, not what changed.
To enable the beta, make sure you have version 2.1.4 installed on your Mac. You can check the Updates tab in Mac App Store if you bought the app there. Alternatively, open Fantastical's preference pane (File > Preferences) and click on Update > Check for update if you purchased the app directly from Flexibits.
With the app updated, go into Fanatical's preferences pane and click on the Accounts tab. Select your Google calendar account from the list of available accounts, then hold in the Option key on your keyboard. Click on the dropdown next to "Refresh calendars" and a new Push option will be available; select it.
Repeat the process for any and addituonal Google calendars you want to test on.
Going forward, any changes you make to your Google Calendar should be synced in near-real time. I've tested it from an Android device to my Mac, and changes are showing up within about 3o seconds or so. Far better than the 5-minute refresh rate I had before.