If the start time is >=12, it is supposed to be subtracted from 8pm meaning: 20:00:00- start_time to find how much time is there.
So, if the start time is "2019-01-22 16:37:45", the time is 03:22:15.
The reason I want this time is because I have an SLA ticket, which takes 8 hours to be completed. And the business hours is until 8pm. So, if the ticket is raised later than 12pm, it will have to continue the remaining time the next day. That is why i want to find out how much time remained after 8pm.
So for the start time of "2019-01-22 16:37:45", the workers end work at 8pm, leaving 03:22:15 hours remaining to continue the next day 8am.
So the SLA should end on 2019-01-23 11:22:15