It also depends on the branch. If you are AF and going to UPT you can expect up to a yr wait before going AD.
Here's the rule of thumb. SA grads go first, then ROTC grads go according to date of rank. Thus, if you graduate June 1st, all of the SA grads go, and all ROTC May grads go, then you go.
If you are going to a competitive slot with limited school dates, you can easily see how it will take months before you go AD. For example, UPT bases usually start up classes about every 4-6 weeks, additionally there are only a select few bases that offer the classes, thus it is a long wait. Currently, there are AFA grads not going to UPT for 6-9 months. SA grads will go AD on casual status. ROTC grads will not, in other words, find a job at home for at least 9 -12 months.
Best way to find out the timetable is to research it on the SA side from cadets going that route. If they are saying they are going the week after commissioning, then the chances are you will be a month or two out. If they say they aren't entering their "school" until Sept., then don't expect to enter until Dec.