It is very difficult to say when the tradition of Ganga Aarti started. However the Ganga Aarti at Har Ki Pauri was started by Pundit Madan Mohan Malviya in 1910s. Recently he was awarded as "Bharat Ratna" highest civilion award by Indian Govt. The small island infront of Har Ki Pauri Ghat is named after him.
Ganga Aarti Timings
Ganga Aarti is organized two times in a day, morning (at sunrise) and evening (sunset). Starting time will depand on sunrise and sunset timing at Haridwar. Morning Ganga Aarti is not as famous as evening one. Approx timings of Ganga Aarti you can see in below table. Minor diffreance of +15 mins or -15 mins can happen. You should reach at least 45 mins before the aarti time for morning Ganga Aarti and 75 mins before the evening Ganga Aarti Ganga