For maximising muscle growth(Hypertrophy) you need to make sure that you're keeping higher time under tension which will incorporate more muscle fibre against the resistance and incur in a much better growth.
A prolonged muscle time under tension, only when fatigue leads to full motor unit recruitment, affects the acute amplitude of muscle protein synthesis and mediates a delayed effect on rates of synthesis during 24–30 h recovery. Provided your protein intake is to the point. Time under tension Reference
Therefore, increasing your time under tension to about 40-45s will be optimum.
The reason you shouldn't look for reps as a rule of thumb is exemplified here. Consider these three cases for Bicep curl(This is applicable to almost every exercise):
1 rep: 1second concentric(lifting the weight up)+ 1 sec pause for squeezing the muscle + 2 sec eccentric(lowering the weight)
Time per rep = 4sec. Reps required for optimum time under tension = 10
1 rep: 1 second concentric + 2 second eccentric
Time per rep = 3 sec. Reps required for optimum time under tension = 13(~12)
1 rep: 1 sec concentric + 1 sec pause + 3 sec eccentric
Time per rep = 5sec. Reps required fo optimum time under tension = 8
On a personal level, I have experienced more satisfying workouts after incorporating these techniques.
Hope this helps.