how long between rest should it take

never. : )

The body and brain aren't releasing Oxytocin or Prolactin so there's no refractory like from a Trad-O. There's no discharge of semen, dis-engorging the GU system components (prostate, vas, seminal vesicles etc.) From a mental and desire point of view, one O tends to beg for another -- hence the label of Multiple Male Orgasms.

Like any athletic endeavor, the bod has to restore glycogen to muscles to support more exercise.

My visual-Os are accompanied by humming feelings that don't consume too much physical energy. So after a two hour session with perhaps two major visual Os, I'm craving and capable of more following a 90 minute break.

Orgasm that drives major muscle tremor gobbles up glycogen rapidly. Cardio action also saps up body reserves and there's also a need for hydration due to sweating. I'd liken 45 minutes of MMO with heavy muscle tremor to a mile of jog. However the high is different since it's not just endorphin driven -- there's a lot of brain action eating up sugars as well.

Bring 'age gifted' I don't have as much endurance as a younger guy and if I'm under-hydrated going in, I get ugly cramps. I then need a good night's sleep to be pain-free. -- remember YMMV.