I recall attending the New York International Conventions in 1958 and 1961(?) as a young child. Each day began with actual "sessions" at 9:00 am, after breakfast being served in big tents. There were long lines, but the cost was ridiculously low (about 35ยข) and the food was pretty good. The sessions ended about 9 at night. Everybody's brain was frazzled. I don't know what they were thinking when they decided to subject the "friends" to 8 days of unending indoctrination.
One thing I clearly remember about the 1958 convention. One of the speakers went on and on about how IF this old system lasted another 10 years, highly unlikely, then there were ONLY so many meetings till the end and how we couldn't afford to miss any. That was over 55 years ago. The Organization now bears little resemblance to the one back then. Almost every major belief has been changed. Now the whole thing is run by lawyers and bean counters. Everything is set up to protect the Organization and its assets. Reason, common sense, and humanity be damned.
I believe the field service thing was part of the conventions back in the 30's or 40's. Then they tried to revive it in the 70's. I don't recall it being a part of the 1958 or 1961 International Conventions. But hey, I was very young. Maybe I just don't remember it.