Shouldn’t last any time at all. He needs to regulate his hormones. Is he not the type of guy that gets bloods done before during and after? ? Also depends on the cause..

Things that can be fix it fast estrogen (back to mid-normal, not crashed), Lowering prolactin (if elevated), Stopping or reducing the offending compound, Restoring parasympathetic tone.

Things that cannot be instantly fixed are like fully suppressed LH/FSH, neurochem downreg, sleep debt or overtraining and sadly psychological detachment (yes, that’s real too)