The earlier the better if you plan on being in for the long haul and have to figure in timing to hit your marks and make it to your DH tour on time without a lot of tour-length monkeybusiness in between. If you get yourself behind your yeargroup too far in terms of progression, and then other delays creep up on you, you can find yourself in a hole nad having to play catch-up. Not a good spot to be in. It would take a while to explain all of what I am getting at I guess, but I was in that situation (elected to start API after a comfy break), getting my wings took longer than I thought, got behind, shore IP tour went from 33 months to 23, and that was longer than they wanted to let me stay. If you are staying in, the navy will roll you early from shore duty in a lot of cases anyway, and the further behind you are the earlier that will be. There are a lot more factors that making starting earlier good career-wise as well, but that is one example.