There are way too many factors to give any sort of hard and fast rule as to how long it takes. Honestly, there are a lot of environmental and personal factors:
-your support group
-your mental stability at the time of the break up
-any/all abuse involved during, before and after the break up (which can exasperate getting over them)
-the seriousness of the relationship (notice this doesn't necessarily mean the quanity of time spent together, though that can be a factor)
-the emotional, physical, and financial investment you had in the person
etc, etc...
personally, my first boyfriend in high school...got over him in a couple of days (we were together a month, I dumped him)
last boyfriend, took me about 6 months...and there was a lot of abuse involved (together over 5 years)
The reason people give timelines for this stuff is because it's comforting...and most people, psycho-socially pretend they're over things much sooner than they actually are because they want to conform to the social norm as it's seen as weak or "hung up" for it to take longer than expected...you just have to do it in your own time...
What will help speed it up:
-go see a therapist
-maybe an anti-depressant if it's really bad (i.e. suicidal thoughts, anxiety etc)
-force yourself to spend life as usual (as much as humanly possible) and go out and still socialize...sitting at home is the worst for a situation like this
-talk to others who have been through bad break-ups and can empathize...it helps...
-being patient with yourself
On average, it takes 2 years to grief a major loss (death, loss of a friendship/partner, income etc)...that doesn't mean you can't move on before that, but they're still be some hiccups along the road. A major break up is a grieving process just like any other. And that grieving process goes for you being the dumpee or the dumper...you both have to grieve the loss.