Translation:Shulchan Aruch/Orach Chaim/286
Laws of Musaf on Shabbat
Seif Katan 1) The time of the musaf prayer is immediately after the morning prayer, and one may not delay it more than seven hours in to the day, and if one prayed this service after seven hours one is called a sinner, despite the fact that he has fulfilled his obligation, since its time is the entire day. If one forgot and did not pray until its entire time passed, it has no replacement (prayer). And raising hands (for the priestly blessing) takes place during musaf. Rema: And if one said the musaf prayer before shacharit, he has fulfilled his obligation. (Rashba, Riy on Tefilat haShachar)
Seif Katan 2) Every individual is obligated to say the Musaf prayer, whether or not there is a community in the city. Rema: And afterwords, the leader of the congregation repeats the prayer, as in the other prayers. Beit Yosef in the name of the Shibboley Leket.