Then and now, studio time varies wildly depending on production approach, arrangement, the number of takes required to get a "keeper", and the opinions of stake

Then and now, studio time varies wildly depending on production approach, arrangement, the number of takes required to get a "keeper", and the opinions of stakeholders who may wish to keep working. So estimates are hard to make. Many artists basically craft tracks in the studio these days. That really started in earnest with Sgt. Pepper's but it's much more common because of democratizing technological changes. You can spend unbounded amounts of time in the studio if you have the budget.