The anniversary of Rochester and Bertha's wedding is well known, as it's explicitly stated in Chapter 24, when Mason declares, "on the 20th of October, A.D. – (a date of fifteen years back) Edward Fairfax Rochester, of Thornfield Hall, in the county of –, and of Ferndean Manor, in –shire, England, was married to my sister Bertha Antoinetta Mason" (Bronte 338).  The year must be approximated based on an estimation that Rochester and Jane's failed wedding ceremony takes place in 1808, fifteen years prior to that would place Rochester’s wedding with Bertha in 1793.  

Bronte, Charlotte. Jane Eyre. Barnes and Noble Classics, 2003.