Hi Philipp,
Thanks for getting in touch with us with your question.
That part of the search results is not handled or generated by us to the best of our knowledge.
There could be some setting in Google My Business that lets you add that information like the opening hours.
I was digging a bit further into this. What I found that on the sample website you shared the list view of the calendar is the only one that lists the 3 events and nothing else. That could potentially be the source of it. Might be there is an option to add the url somewhere in Google My Business.
I hope this helps somewhat.
Is there anything else I can help you with?
Cheers,
Andras