I don't let a heavy orange or red covering of rust appear on the bbls or parts before boiling.
It's not necessary.
It will of course produce a rust blue.
But for a layer or cycle to produce color after boiling, it's not necessary for that heavy accumulation.

I don't let the parts rust very long and like Lefusil states you can barely see the rust sometimes and they are ready for the boiling water.
The place where I hang bbls and parts is kind of dark, so I generally judge them as being ready (or not) by very gently dragging my finger tips down the surface.
If I can feel the drag of a coating formed,,they are ready. Feels about like a new piece of 800grit paper you are touching.

I know that goes against all the 'Don't ever touch the parts' advise. But I've been able to do that w/o any problem.
Dry hands,,what ever. I don't do any other handling of the parts during the process w/o wooden attachments or metal hangers.
Just that one very gentle touch to check if they are ready.

I think a lot of people assume the heavy rusting coat is necessary for rust bluing. Maybe that comes from seeing it used to do rust browning on Muzzle Loader bbls and parts.
They usually let them rust up pretty good. Seems like More is Gooder in that area.
If you want the matted look that's OK too. Sometimes it fits the piece being redone.
But it's not a necessity for a layer of color.

Express Rust Bluing , each swabbed on coating of soln produces an extremely thin layer of instant Rust. That in turn produces Blueing color just fine with every boiling cycle.
Why would there be a need for heavy rusting when doing Cold Rust Blue.