Hey @Charlie_Richardson & @Zuad_Oropeza1
Interesting workaround to your Organization’s vacation needs, however at this point this is not possible. There is no way to restrict the creation of Tasks that are assigned for a certain day, nor according to resource allocation (which is what Zuad is looking to do).
What we do here is create a Project that’s home to Tasks with titles that schedule vacation days to help our Team stay on track. This allows our team to reference who is out of the office and at what times, which we police ourselves. That said, there isn’t a way to enforce this via the system in Asana.
This is an interesting idea though. I’d encourage you to make a quick search to see if someone has already made this suggestion in the Product Feedback category so you can up-vote it