CARIUS TRAINING GUIDE
Rest long enough to perform the next set at the quality your goal requires. Heavy compound strength work generally benefits from longer recovery than small isolation exercises or conditioning-oriented work. If short rest causes your repetitions, load or technique to collapse, the rest period is probably working against the training objective.
Do not confuse feeling exhausted with having trained effectively. For a heavy squat or bench set, several minutes may be appropriate. For lighter accessory work, shorter rests may be adequate.
The practical test is performance: are you recovered enough to execute the next prescribed set well?