The short answer
Adding business days is a calendar rule, not just adding hours. Define the working week, holidays and time zone before calculating a date.
Define the calendar first.
Choose the working days, the time zone, and which holiday calendar applies. Decide whether the starting day counts and what to do when the input falls outside working days.
Keep the policy separate from the workflow.
Put the date calculation in a reusable helper. Pass the workflow values into it, then format the result for the HubSpot field or action that will receive it.
Fri
Start
Sat
Skip
Sun
Skip
Mon
Day 1
Tue
Day 2
Assumes a Monday–Friday week, no holidays and a starting day that does not count. If Monday is a holiday, the result moves to Wednesday.
Test the dates people trip over.
Cover weekends, holidays, month and year boundaries, and your chosen time-zone behavior. Include missing dates and a zero-day offset.
If you’re using Turbyn
If you build this as a Turbyn action, keep the calendar helper and its dependencies together. Map the starting date and offset from your workflow, then test before publishing.
Turbyn setup guide