SLA Calculation Enquires

i was using 1.18 version. i have created a SLA Plan grace period is 24.
i try to create a ticket on 2024 June 25 3:16pm and selected the SLA Plan.

The Due Date show on the ticket is 2024 June 28 12:16pm

Please assist.

Thanks in advance for your reply.

What does SLA have set as Schedule?
How is the used Schedule set up?

Try:
Create a new schedule. Type set to Business Hours.
Do not create any Entries or Holidays.
Set this schedule for your SLA and test it.