There are 60 minutes in an hour so 1 hour 20 minutes = (60+20) minutes = 80 minutes
He will spend a total of 80+10 = <<80+10=90>>90 minutes
90 minutes is = (60/60) hours and 30 minutes = 1 hour 30 minutes = 0130 in 24-hr time
He has to leave 0130 hours earlier than 0900 i.e. 0900-0130 = 0730 hours
#### 730