Work-Relay dates calculations can be performed based on the Salesforce Organization Business Hours setup. Business Hours record id has to be provided in Work-Relay  Settings.

Please follow the instructions below to set up new business hours record and link it to the Work-Relay.

Open Setup (administration page) > Company Settings > Business Hours:

Create new business hours record or choose one out of existing records.

Please refer to the following article for the instructions on how to create Business Hours property: Set Business Hours.

Navigate to Settings tab and switch to General Settings subtab:

Choose your Business Hours item via Business hours lookup (1) and click Save (2). Now this business hours property will be applied to all Work-Relay processes in the current organization.