How to use Table.Buffer , List.Buffer or another method to load data faster?

[SantiAdvent]

I have a large dataset and I created a custom function to get the networkingdays. The Holidays list is a list I have with the Holiday dates listed.  I then create a custom column Networking days(OrderAddDate, OrderShipDate, Holidays) To give me the turn around time in days taking out the weekends and the holidays. I then have to replace errors and 0's with null. This is taking forever to load. 

Can anyone help me speed this process up please?

[SantiAdvent]

Could you elaborate on that? - I'm relatively new to  DAX & PQ. Thank you.

[lbendlin]

Use the NETWORKDAYS function in DAX, or have your working days clearly marked in your static calendar table.