He was also required to do 750 hours of community service and pay a USD 5,000 fine for his disorderly conduct, reported Ace Showbiz.
The Hilton heir pleaded guilty in March to a misdemeanour assault stemming from a meltdown aboard a British Airways flight from London to Los Angeles on July 31, 2014.
He allegedly yelled at the flight attendants and the 21-year-old threatened them too.
According to an affidavit written by an FBI agent who investigated the disturbance, Conrad was restrained and handcuffed during the flight after calling some passengers "peasants" and threatening the flight attendants.
After the mid-flight outburst, Conrad voluntarily checked into a 30-day inpatient drug and alcohol treatment program in February.
Conrad's attorney, Robert Shapiro, claimed that his client's disruptive behaviour was "the effects of a sleeping pill".