“ Musaf can be said all day. Rabbi Yehudah says only until seven hours into the day
Explanation
Hours: In Jewish law, an 'hour' is one twelfth of the day (or one-twelfth of the night) . Thus, the actual length of an hour varies somewhat depending on the latitude and the current season. There are two opinions about when the day begins and ends: the Vilna Gaon says the day starts at sunrise and ends at sunset. The Magen Avraham says it starts at dawn and ends when 3 stars come out. Midday is, thus, six hours into the day, rather than noon. ”