Given that you have completed the build place process is completed. The upgrade process should be able to completed by 5-6 hours.

What time is involved in the build place process?

It will take at least 3-4 days.

Does that go on in the background or is that 3-4 human time?

There are series of steps to be followed. Some steps will run in background for some time after manual execution. 

@EILCTHOMPSON , I can second this (3-4 days). There are several steps you have to start and it will run online (applying Release update, running sanity build, & creating a delivery environment). The online services will do most of the work. Nowadays in the upgraded documentation you have a pretty good idea of the steps you'll have to go through. 

Release Update Studio - ALE Documentation For IFS Cloud