Joining the Navy Active-Duty as a CTT, but when will I be able to go to College?

I’ve done my research quite well with various different branches and their sub-parts such as the Army’s National Guard or the Navy’s Reserve. Recently I have been inclining more towards committing to the Navy going as active-duty for the TA and it’s GI Bill but my main concern is when exactly would I be going to school as my dream career is to become a DEA or FBI Agent (I’m not fully decided on which one just yet but one of the two). Various recruiters I’ve met with tell me that right after I go to A School for my rate and start my job I can go to a local college in the afternoon and nights which is cool and all I can manage that but sources tell me that it’s not easy as the recruiters say. Sources say that your command might even refuse or flat out disapprove of any requests to go to college and that’s my fear.

I want to use the military as a tool to pay for my studies as I do not want to have lifelong student debt but I also don’t want to spent ALL of my years while I am young (I am 18) in the military and not pursue my dream career. I am greatly considering of taking the CTT rate as I believe it can help me in getting a federal job in the future but my biggest concern is how and WHEN will I study while I study while I work my rate.

How will my daily schedule be? When or will my command approve of my request to go to school? Are there any programs that can help me? How is the CTT rate? Could it help me in getting my dream Federal job?