How long does it take for transfers from old iPhone to new iPhone?

The transfer depends on how much data needs to be transferred.

If you have text messages that contains lots of photos and/or videos, those need time to transfer.

Then there are your pictures, music, movies, etc. to consider.

All of your settings, apps, widgets, browser extensions, etc.

Unless you clean up by deleting lots of unnecessary data beforehand, this could easily take several hours to complete.

It depends how many apps, photos, documents, etc you want to transfer. From 10 minutes to an hour or more