Usually the manufacturer of the floor finish materials will have a recommended schedule.

Hi, what if the wood is coming from a mill? There isn't a manufacturer name.

Thanks!

I just found these directions on the Minwax site, which says that if the floor is not stained, add a third coat, leading me to conclude that a stained floor doesn't need as many coats.

1. Sand floor as appropriate for the type of floor finishing project. Carefully follow label directions and the directions for the sander that you are using.
2. Remove all dust, then thoroughly wipe the floor with a clean cloth dampened with mineral spirits and allow to dry.
3. Before use, stir Minwax� Super Fast-Drying Polyurethane for Floors to rotate the product from the bottom to the top of the can. You will not need to stir again if the project will be completed in one day.
4. Apply a thin coat using a lambswool or synthetic pad applicator, or a natural bristle brush. Maintain a wet edge to avoid lap marks.
5. Let dry at least 3-4 hours until film is no longer tacky to the touch. If allowed to dry for more than 12 hours, sand lightly with 220 grit sandpaper, then wipe floor with a cloth moistened with mineral spirits to remove all dust.
6. Apply a second coat of Minwax� Super Fast-Drying Polyurethane for Floors following steps 4 and 5.
7. If the floor was not stained, apply a third coat of Minwax� Super Fast-Drying Polyurethane for Floors following steps 4 and 5.