It seems there is a new theory emerging on the best timing of cord clamping.  In short - usually it is done immediately (meaning within a minute) of the baby's birth.  Scientists and doctors now believe there is a great benefit to slightly increasing the time between birth and clamping.  

"The main benefit [to delayed clamping] is increased iron to the baby," he added. "That is done by three minutes or so." 

Read the article here.  

And most importantly talk to your doctor and midwife.  And make sure to add it to your birth plan if you decide you want it.