When working with calculated fields within SharePoint, there isn’t an inbuilt function that will allow you to add a specific number of hours to a date. You have to stop of a second and think about it – and the solution is quite simple.
While adding whole days is as simple as =[DateColumn]+5, to add hours you have to break things down. So to add eight hours…
=[DateColumn]+(1/24*8)
See this helpful blog post for more information.