So my friends and I just finished putting down the last deck plank
last night.

The deck looks great, but the damn lumber yard has spray paining all
over several of the boards.

Should I sand this off before I begin staining the deck, or will it
wash off with a power washer?

Second, how long should you REALLY wait before staining? I have heard
answers from 12 months, to 6-8 weeks.

Any help is appreciated. Thanks!