The simple answer is never. Rails to Lake Mahopac were abandoned before Metro North was created.
IF you are thinking historically, here's a brief summary. To reslly understand this, you should refer to the 1928 topo map. Here's the link docs.unh.edu/NY/cfls44nw.jpg - the NW segment of the Croton Falls quadrangle.
On the Punam Division, thre was a station in Mahopac. The 1905 employee timetable shows "Harlen R.R. Crossing" 1.15 miles south of Mahopac station.There was a branch of the Harlem Line from Golden's Bridge to Lake Mahopac, crossing the "Put" at that location. It's original station in Mahopac (named "Lake Mahopac") was at a somewhat lower level slightly to the west of Mahopac on the PUT.
