At this point, I think the easiest way to do this will be with Webcore, which can handle much more complex automations than the official app, including calendar-based ones.
It’s very popular: so popular in fact that they have their own forum. It’s a little complicated to set up, but there are lots of people over there who will be glad to help you, and to help you design this particular automation.
See the community FAQ. (The topic titled is a clickable link)