I'm not sure what to pick as my answer. In some cases it took me a month or so. However, when I broke off my engagement it took less than one day. As you said it depends on the circumstances. I knew that my engagement was bullshit about 6 months before I broke it off. I was with jj the same day that I broke off the engagement. My family called it a rebound, but if that's what it was it's a rebound that has lasted 7 years with 4.5 years of marriage.
The typical rule of thumb is that it takes half the time of the time of the relationship...
1 month=2 weeks
6 months=3 monthsf
etc.