Time estimate for reaching 155F for baking 9lb Turkey breast

You can absolutely cook a turkey without a wire rack. I have done this for years.

What I suggest is laying down a grid of celery and carrot sticks, to elevate the turkey a little bit and keep it from sitting in the juices that will come out during cooking.

These aromatics will then lend their flavor to the pan drippings, and help you make a fantastic gravy.

Another approach, which I do not like as well, is to crumple aluminum foil into a snake-like shape, and coil or snake it around the pan to serve as a makeshift rack.

This works well, but doesn't offer the flavor benefit that using aromatic vegetables does.

You don't judge cooking time. You measure it with a thermometer and get it out when it is done, as indicated by internal temperature.

All estimates of cooking time based on weight are not precise and will frequently lead to over- or undercooked meat. If you insist on using such an estimate, it doesn't matter much if you use the weight before or after marinating, as your error will be larger than the variability caused by weight difference. Choose whichever weight you want to.