Vince Gironda's old 30 second idea.
Used in the 60's and beyond. And usually with the same weight in the 8X8's or 10X10's per exercise style, as was Gironda's original intent. ..60 to 90 seconds was the normal pattern than between sets. Including those 18-20 plus high volume sets.
Have no doubt Weider's claimed it as their own super secret workout plan along the way.
Good Luck.