QUINCY — The development company poised to turn the Quincy Medical Center site into a massive residential complex says demolition of the hospital buildings is set to start in March, and construction should begin in mid-2021. FoxRock Properties, owned by Granite Telecommunications CEO and Quincy native Rob Hale, recently released updated projections for its Ashlar Park project, which includes 465 apartments spread over seven buildings as well as 590 garage and ground parking spots on the 15-acre former hospital campus. The Hospital Hill project will have been in the works for roughly five years by the time demolition begins, a timeline that has become a sore spot with city residents and officials.