Time in press is longer or shorter based on thickness - the heat has to transfer from the press plates (platens) to the center of the board. As wood is a natural insulator it takes some minutes (say 5-15) even with plates around 500F. Modern presses are also continuous with large heated moving bands, top and bottom, doing the pressing as the MDF travels through the equipment. Saws trim the edges and a flying saw moves across the sheet to cut it to length. The panels then set in big cooling racks before getting stacked for shipment. Waste gets reground and fed back into the process. There are some YouTube videos you can watch to see these in action. Particle board and OSB are made in a similar fashion.