计算工作日/小时左右的日期？

I am currently working on a website to track projects. In it, it is possible to create Service Level Agreements (SLAs). These are configurable with days of the week that a project can be worked on and also the timespan on each of those days. Eg. on Monday it might be between 08:00 and 16:00 and then on friday from 10:00 to 14:00. They are also configured with a deadline time depending on priority. Eg. a project created with the "Low" priority has a deadline time of two weeks, and a project with "High" priority has a deadline of four hours.I am currently working on a website to track pr