A Whole Salmon Fillet takes around 12 minutes to fully cook and you should check the Salmon Fillet often while it's cooking.
Here's how I cook my Salmon Fillet.
Preheat oven to 475 degrees. Place butter on a rimmed baking sheet and season with salt and pepper.
Carefully remove the baking sheet from the oven and place the salmon on top of the butter with the skin side down; season with salt and pepper.
The salmon should be fully done and cooked through within 12 minutes.