He makes it in batches of 1.5*128=<<1.5*128=192>>192 ounces
He drinks 96/2=<<96/2=48>>48 ounces of coffee a day
So he drinks the coffee in 192/48=<<192/48=4>>4 days
So in 24 days he makes 24/4=<<24/4=6>>6 batches
That means he spends 6*20=<<6*20=120>>120 hours making coffee
#### 120