This is with Horae enabled. The timeline itself was created private and it added my default subscriber group automatically. However, the events were all created public which would not be visible (and the default subscriber group was not added as well...). This should also consider the forced private setting in public worlds!
Ok, historical events now inherit your world's privacy setting and default subscriber groups on creation. They also respect the forced private setting. Let me know if I missed anything.
Closing this since I haven't had any response in two weeks. Feel free to message me here if something is wrong.