What I've learned ( on the hard way ) is that soap will degrease the barrel and it starts to rust from that second on you did the first pull through.

Its of course not much, but the surface inside the barrel will become bigger and rust become more every time.

To use an oil-emulsion ( hot water + a suiting oil / solvent ) is far saver and works astonishingly even faster.

Also its an advantage to use compressed air to dry the barrel entirely before its oiled to put it away.

I'm now down to 15 minutes on my Hawken

Cheers Jochen