What is the waiting period for Active Duty Army Enlistment?

I am going to be seeing a recruiter soon and start the process of enlisting in the Active Duty Army. I am just curious as to how long I will have to wait, until I can ship out to BCT. If I get the MOS that I want, and there is an open slot, can I go as soon as possible or does everyone have to wait a certain time? By the way, I want to become either a CAV Scout, or an MP.