If music is a priority for you, you will find/make time for it (AFTER Plebe Summer). The Glee Clubs and Gospel choir all need accompanists. Women's glee club has two official rehearsals per week, and more (sometimes every night) in the week leading up to a major concert or other event.
Many Mids keep musical instruments in their rooms, such as a guitar. A keyboard wouldn't take any more space than a guitar, and your parents could bring it to you for PPW.