My first long interview was with Bill Tiller.
I told him in advance that I have a lot of questions and he said that it's not a problem.
I ended up skipping tons of questions because his lengthy answers answered a lot of them (without me asking).
So that ended up being 4 hours.
From that point on, I started informing people that the length of the conversation is up to them.
They can give me shorter answers or very lengthy ones, either way I will not interrupt them and I will not edit their answers in any way in the final edit.
From that point on, my interviews started being 3-4 hours long each.
Usually, when people are interviewed, they want to answer the questions properly without taking over the conversation with 20-30 minute long answers.
I make sure that they are aware that I'm perfectly comfortable with longer answers.
Most guests are surprised by how long my previous conversations were, only to end up talking just as much or even longer.