Have you considered this instead?
Calendar Notifications & Actions - Blueprints Exchange - Home Assistant Community
I think this might be what you’re looking for? Or at least you can use it to help update what you have here to make what you want work?
I would say most likely better to just use the trigger like a calendar event for the time of start? Fire the other actions? And if it’s a shared calendar, then you can add additional keywords to look for to filter things out?