I'm posting my solution for this common issue here in the hopes to help other users who have similar requirements to assign Flexi-tasks to users on Business Days only. I had seen on nintex community that there was a UDA created for this but it didn't work properly for me (due dates were just blank). I am using SharePoint 2013.
Here is my manual workaround that has been working very well for my workflow:
I hope this is helpful, please put any questions or comments below
Solved! Go to Solution.
Thank you so much for this, it took me awhile to locate this thread/solution. This really saved me some time and pain