Mojave: Default start time of new events
You can choose the time to start / end your day with macOS Calendar - it's in the general setting.



For specific events, Calendar app should do natural language scheduling like many third party calendar apps have done for quite some time.


https://flexibits.com/fantastical


Fantasitcal has a free trail and is worth every penny in my experience, but you can use native new event controls to just make your appoint for the date and time of your chosing. Siri will do this as well for you, you just need to be in a place where you feel comfortable speaking to your Mac and enable Siri.


  Make an appointment for next Wednesday at 11 am




And with the text above, you should see this completion (for the next few days at least when another next Wednesday will be selected).