Use of hairdryer to loosen stuck focus - proper practice?

I have read here where some have used a hairdryer to loosen stuck focus on MFs, like Agfas, as a first step towards cleaning and refitting.

What is the proper way to go about it?

- steady exposure and built-up of heat?
- or cycles with cooling steps?
- multi-day application?

I plan on applying the hairdryer method to an Agfa Ventura (U.S. issue off the Isolette family), and I already made a cardboard "heat shield" to protect shutter and bellows..