* Late 17th to early 18th centuries: While specific documents naming a "Master Mason" degree as we understand it today are elusive from this period, this era saw the development of operative masonry traditions evolving into speculative masonry. The transition involved incorporating symbolic and ritual elements that eventually formed the basis of the degree. Evidence suggests the hierarchical structure, with progressively more advanced levels of knowledge and ritual, was taking shape during this time.
* Early Grand Lodge era (1717 onwards): The formation of the Grand Lodge of England in 1717 marks a pivotal moment. While the exact structure of degrees may not have been fully standardized initially, the establishment of a governing body facilitated the codification and spread of Masonic rituals and degrees. Though not explicitly stating "Master Mason" as a distinct degree in the early constitutions, the hierarchical structure implied its existence.
* Mid-18th century onwards: By the mid-18th century, references to the Master Mason degree become more frequent and clear in lodge records and published Masonic texts. The degree's structure, rituals, and symbolism had solidified significantly, resembling the form we recognize today.
In summary, pinpointing the *earliest* reference is difficult due to the gradual evolution and lack of complete historical records. The period from the late 17th to the mid-18th centuries represents the crucial timeframe when the elements of the Master Mason degree emerged and solidified within the developing structure of Freemasonry. Finding a single, irrefutable "earliest" document is unlikely.