Consistency creates the sequence
If one set rests 20 seconds and the next rests two minutes, the effort pattern changes. A consistent interval makes later-set performance comparable from session to session.
Upper-body isolation work may use roughly 20–30 seconds; demanding leg work may require longer. The target muscle and stable execution decide.
Progress the completed series
First, complete more of the planned repetitions across all sets at the chosen interval. When the whole series is controlled and the pump remains strong, add a small amount of load.
Reducing rest can be an optional density experiment, but it is not presented as Nubret's universal progression rule.