Having now read the above linked masters thesis completed in 1959 by a student at the University of Richmond and specifically about the history of the Danville Military Institute ("DMI") and using a bit of deduction, ring style and trends of the times, we can probably narrow down to possible years of this rings manufacture.
The thesis does a fairly good job helping put together the often disjointed history of the Danville school, it has beginnings as early as before the Civil War but it really does not gain traction and is never officially called the Danville Military Institute until its founding in 1890. Its not officially accredited by the governing educational bodies of the era until 1896 and it goes through several transitions between that time and its ultimate demise in 1939. Several of these transition periods saw the school change names entirely.
What I will call (as the thesis author did) the "glory years" of DMI is from 1890-1902. As the school was on a 4 year curriculum its probable that the first possible date for the class ring is 1894 though due the fact the school was brand new and not even fully accredited by 1896, it's unclear whether the first true graduating class in 1894 received rings or not. So we have the first period of the ring as being roughly 1895 to 1906 as the schools founder left the school by 1902 and it continued as DMI for a further four years to 1906 when ownership changed hands and the name was changed.
The school again was called DMI from 1919-1932 and finally, briefly from 1936-1939 after which it was permanently shuttered as a military institution according to the thesis.
Looking around at other school class rings from all three periods (1890-1906, 1919-1932 and 1936-1939) and specifically looking at other military schools like VMI, West Point and Annapolis (and taking into account the curriculum at DMI particularly was catering toward prepping students to go to USMA or USNA) my guess would be this ring was made during the second period of DMI (from 1919-1932). I found a USNA ring from 1916 (below) and there are some similarities in the eagle design and placement as the DMI ring. Not saying its the same but I would not put it past the powers that be at the time to model the new school's ring on something like this.
Wonderful old ring! 
Andi
