I've heard Dr. Harley say about two years of dating. If there's still no move toward marriage after about two years, it's probably time to break off and date some other people.

Married-14 years
NC- 14-Apr-11
1 DS 15
Online course July '11 to July '12
17 sessions with S. Harley Feb '12 to Sep '12
Divorced Jan 21, 2013