Pre-Millenial conferences were Bible conferences with a special focus on biblical prophecy and a pre-millenial. They are closely related to prophecy conferences, study meetings popular among late nineteenth century evangelicals. In addition to the theological work done there, these conferences were important as social networking occasions for conservative evangelicals from various denominations and organizations. Pursuing their mutual interest in a major biblical doctrine, they found that many of their denominations and institutions were facing similar incursions of modernism.
The greatest of the prophecy conferences was the Niagara Bible Conference, which met annually from 1876 to 1897. According to the Henry Manuscript, Lyman Stewart attended this meeting as part of an effort to find a qualified assistant pastor for his home church, Immanuel Presbyterian Church.
Biola organized its own regional Pre-Millenial Conferences. The one held in June of 1910 in Santa Ana involved multiple speakers at multiple churches: On Friday night, T. C. Horton spoke on "God's Plan in the Ages." On Sunday Mark Lev preached "at the U. P. Church" and Mr. Shelley preached in the Baptist Church. In the afternoon J. H. Sammis spoke at the U. P. Church, and at night R. A. Hadden spoke at the Presbyterian Church. "The meetings were all well attended and there is an increasing interest in prophetic subjects."
http://www2.biola.edu/kingsbusiness/view/1/7/17
(note need to standardize spelling of premillenial, pre-millenial, Pre-Millennial, etc., especially owing to nonstandard spelling of it in our own source material)