Normal length of time taken to arrive at a phd admission decision?

I would like to know, if possible, how long it takes on the average to reach a first admission decision for doctoral programs?

Let us say a doctoral program promises to inform the applicants of the outcome three months after the deadline for submitting application packages. Does this really mean that to reach a decision requires exactly three months? If you have experiences in such a process, please share me with the things that actually would happen.