Before Grilling the ribs you should place them in the oven on a roasting pan and bake the ribs until the ribs become tender.
It takes 1 hour to 1 hour and 15 minutes to bake ribs till they're tender and then you can transfer the ribs to the grill to cook further.
You then grill the ribs 15 minutes per side for total of 30 minutes grill time.