In the future when you create events from within an email (etc.), you should find them stashed inside of your chosen app. Select it, then choose the application you want to use (such as Fantastical or Things).
How to use a different calendar applicationĬalendar on the Mac has a little-used Preference that lets you change the Default Calendar App used on your Mac. You can set Calendar up to open multiple files you just need to create an alert for each one.
At the bottom of the list, choose Custom. Click the time item to access a drop-down menu that provides other time options.