An interview with Brian May appears in New Scientist this week (subscription required), and he seems to have done an excellent job of relating the experience of working on Bang!.
The three of us would meet at Patrick’s house in Selsey on a Friday night, do a little gentle writing, have a couple of drinks, then hunt for Patrick’s cat, Ptolemy, who is an accomplished escapologist. When we got up the next day we were in the mood for serious work. Patrick shocked us by writing the first draft in two weeks. We all then spent the next two years rewriting it. He was good about it. He didn’t mind at all.