As a Manager, I need the system to give the exact remaining SLA time when a work item is reopened. The remaining SLA should be calculated by subtracting the time already used from the original SLA and must consider only operational working hours. Weekends and holidays should be automatically excluded.

For example:

Original SLA: 24 working hours

If 20 hours were used and the ticket is reopened at 8 AM (with a 9 AM shift start) with 4 hours remaining, then by 10 AM the remaining time should reduce to 3 hours, and after 1 PM the remaining time should be zero.