Etk p. 134 just says "rest" "and "short rest" regarding between each rung. "C&P left, switch c&p right, rest, 2 reps, another short rest..."
P.135 clears it all up, titled "whats the perfect rest interval between sets". It says, again I quote "If vodka is the intensity, and whiskey is the volume, then tequila is the density". See, theres the answer. Tequila!
Just kidding! It also says for strength, it doesnt matter if you take 15 minutes, an hour, or a whole day to do 5 sets. But for building muscle, use shorter rests. He compares very short rets, under a minute, to EDT. And long rests to Naked Warrior's grease the groove method. He explicitly doesnt proscribe a rest length.
Doing pullups in the ladder, I was able to rest 1:1 ish between rungs, 2-4 minutes between ladders, and the heavy 5x5 days were taking well over an hour, pushing 90 min often. Rop is a time commitment for sure!