It is helpful to be able to exclude weekends (and choose custom weekly working days), but this customization should be expanded further. The user should be able to set custom list of days to exclude a non-working days.
I build all my timelines using start dates and task durations, which is possible in the Gantt view, and I let deadlines calculate automatically. However, those task durations should only count true working days, which means avoiding public holidays and company holidays. For example, if my 15 days of production fall over a company holiday window (e.g. my company shuts down Dec 25 - Jan 1) then I need the due date for production to reflect start date + 15 working days = due date. If production starts Dec 15, then the due date should be Jan 12. I manage too many projects and adjust the upstream tasks timing too frequently to manage this manually.
From what I see, all the rules and 3rd party integrations are designed to avoid deadlines from landing on holidays, and will automatically move the deadline to the next non-excluded date. But that will not address the issue and use-case I’m describing.
This feature is offered in Smartsheet, and I imagine it is available in other similar software options. With all the emphasis Asana places on automation, this feature is essential. This feature and similar have been requested since as early as 2017 ( Adding Public Holidays - Content Calendar ) so I can’t believe it’s 2025 and this isn’t available.