Hi, It depends on your prgram i.e. number of days you train for example But the way I see it once will be fine. the thing is that this muscle needs time to recover & if you blast it again so soon you wouldn't accomplish that
I find optimal time for me is 6 days. 7 seems to long, 4-5 not enough. This is assuming you are training for mass, in other words working your chest with very heavy weights for achieving overload. You can experiment with your rest time. If you feel recovered sooner, you may give it a shot, but this is not usually the case for us "clean" trainees. We need more rest time than others. Learn to feel your body. You can still stay lean(cut)with cardio and correct diet.
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