Cooking time will vary depending on the size and thickness of your salmon fillets. Roast until the salmon is cooked through and flakes easily, 4 to 6 minutes for every 1/2-inch thickness of salmon. An instant-read thermometer into the thickest part of the fillet should read 120°F to 130°F for medium-rare or 135°F to 145°F for more well-done.