CH, you may apply at any time. You may have a boss who pushed you. If, as an NCO you decide you want a commission then discuss this with your flt and sqn cdrs. They will advise and mentor, see that you get duties that will help your development and allow you to demonstrate suitability. Then you will probably face a station board. Recommendations will all help but ultimately it is up to you when you get to OASC.
There you will be in competition with direct entry candidates. The board then has the job of comparing the unknown with someone who is a known quantity. That can be a positive benefit or a disadvantage. Direct entry is much the quicker route with commissioning from NCA a n alternative that has allowed you to prove ability.