Depends upon when training seat is available. Meps has listings on when the next training seat for basic. From that you and Meps counselor decide when you want to leave
When you pick your job is when you get your ship date. Every job has a certain ship date. If your job was airplane mechanic you could leave tomorrow, but if you pick air traffic controller you could be leaving in a year. Its all what job you pick.
For people going active duty most of the time they go to MEPS once and sign their contract, swear into DEP, and get their ship date. DEP can last anywhere from 48 hours to 1 year. Once a recruits ship date arrives they go to MEPS a second time and swear into the active duty army. The time between swearing into DEP and shipping out depends on when there is a seat available at AIT for your MOS.