implantation bleeding

Sabrina
For those of you that had it, how much did you bleed and for how long?
 I'm wondering if the bleeding I had earlier this week is implantation or my period coming a week early? Typically my cycles are like clockwork, usually 30 days but this time I got my period on CD 24, which is highly unusual, i typically get late periods, never an early one, but so far tests are negative....