Vision of Sabbath truth was given to Ellen White after she accepted the Sabbath. The more detailed accounts would indicate that James White and Ellen White took their stand for the Sabbath truth at about the time of their marriage in August, 1846, basing their convictions upon the teachings of Joseph Bates as set forth in his tract on the Sabbath truth. It was not until some seven months after this that Ellen White was given a vision at Topsham, Maine, in which she was shown the place of the Sabbath truth in the third angel's message. We are sending you a sheet covering this point. I think the information in this will answer your question fully.
Brochure: "Prophetic Guidance in Early Days", page 10 paragraph d.
It is rather an interesting point that the Lord did not, through vision, set forth that which would take the place of Bible study, but the Lord confirmed the study and pointed out error when error seemed to be coming in.