Answer: Yahushua kept the true Sabbath. Obviously, if the day kept by the Hebrews was wrong, He would have corrected them.
Think about this: His life destiny was to be the Lamb of Yah that takes away the sin of the world. The way He was to do this was by fulfilling all of the types and shadows of the Sanctuary services, and specifically the spring Feast of Passover and Unleavened Bread. These feasts are all reckoned on the Hebrew luni-solar calendar.
Indeed, Yahushua did keep the true Sabbath and He did know which day was correct. In the time of Yahushua, there was no controversy regarding time keeping or what day was the true Sabbath within the Hebrew communities. Interestingly enough, even the Hebrew communities that were scattered in other lands were all in harmony with the entire yearly Sabbath Feast days, as well as seventh-day Sabbath. There is even, in the Bible, a record for the dates upon which the Sabbath and Feasts were kept throughout the entire Bible. Remember it was required that all males attend both the Passover and the Feast of Tabernacles each year. They came from far away and knew exactly when to arrive and they didn't have telephones. All of them watched the heavens, but the moon gave them their specific calendar details. Exodus 12, 19; Leviticus 23
The seventh-day Sabbath was always kept on the 8th, 15th, 22nd, and 29th of each and every month. From Moses to Paul, the only seventh-day Sabbaths that were kept were those kept on these dates with the addition of the Feast Sabbaths, some of which fell on the seventh-day Sabbaths which we call High Sabbaths, and some on their own specific days, and are all Biblical record.
It wasn't until there was serious study into the holy feast days that it became apparent that the seventh-day Sabbaths were also connected to the lunar cycles and their New Moon designations. For example:
If a person follows successive weeks (as in the Gregorian calendar) as the cycle for their seventh-day Sabbath, then the 14th (Passover) followed by the 15th, would be rotating through the week, placing it on a different day of the week each and every year. The Levitical command is that it is to be on the 14th of the month – always. The 14th was always the Preparation Day always. We know this to be true, because of the fact that Yahushua died on Passover, the 14th, which was the Preparation Day, followed by the night of the full moon. This fulfilled to the very letter the specifications of which there are twelve. Refer to the eCourse entitled, "Twelve Criteria of the True Crucifixion date.”