This might be a little overkill, but Home Assistant can do this.

1. Add the calendar to Home Assistant. You don't have to manage it there, but it'll have access.
2. Under Settings - > Devices & services -> Helpers add a helper of the type History Stats.
3. For the Entity, select the calendar you want to track, and the Type would be Time.
4. Next it'll ask you which State to track. Depending on the specifics, you'll probably want to track if the calendar is On, meaning there's something on the calendar. You can track multiple States, but you probably only need On.
5. On the last page of the wizard you'll put start and end times. If you want to track from Midnight until Now, here's what it would look like:

Start: {{ now().replace(hour=0, minute=0, second=0) }}
End: {{ now() }}

You can probably adjust the end time to 23:59 if you want to see what's in store for the day looking ahead, but I haven't tried it.