Hey @London 
It’s not possible to show half-days on our calendar features at the moment.
However, you can vote to have this capability added to the platform here!: Calendar View Feedback
You can always submit any feedback or vote in favor of feature requests through our Feedback Section of the Community: Post Feedback Here!
In the meantime, the HR Requests template from our templates center can be used for vacation request setups:
I hope this helps!
Cheers,
Jenna