Honestly, it all depends. I found out after 10 days, my friend found out the same afternoon.
If they are busy you might not know for a while. Experienced hires (like me) it can take longer as they will be making decisions on level and package which aren't needed for grads.
If there are loads of people for a few jobs, they will take their time and sort through for the cream of the crop.
On saying that, if you are amazing, they will want you and let you know pretty swiftly ;-)