Could this be what she really meant? Not that she didn't have the 20 minutes to physically change the strings, but that there wasn't the time to let them break in? If you were doing 12 hours of sessions every day for the next 30 days before your one day off, when would be the best time to let your flatwounds settle in?
I am breaking in a new set of TI's now and after 2 weeks they are still not settled to where the previous set was. Granted, I haven't played 12 hours per day those 2 weeks, but you get the idea. And I would imagine since she was completely freelance (they all were, as she said, it wasn't considered a "group" until it was looked at historically, so there was no "wrecking crew" at the time) that one bad session, in terms of sound not happening, could affect the ability to get other work. Especially since the way most of those records were being made you couldn't recut a bass part that wasn't working, or when you could, are you going to wait another 30 days or whatever for the player to be available again. So, a very long way to say maybe she means that? I don't know, but I'm sure if someone asked she would answer- she's always been very courteous in any replies to questions I have asked via her site.