How Long Should You Actually Prepare for OASC, AOSB, or AIB?

One of the most common questions candidates ask before officer selection isn't about the exercises themselves, it's about timing. Start too late and you arrive underprepared. Start too early, without a plan, and momentum fades long before assessment day. There's no single correct answer, since it depends on your starting point and how much time you can realistically commit each week, but there are useful principles that apply whether you're heading to OASC, AOSB, or AIB.

Why "As Long As Possible" Isn't Good Advice

The instinct to start preparing as early as possible feels safe, but in practice, open-ended preparation without a defined endpoint tends to lose focus. Candidates who begin a year out with no structure often peak too early, or spend months on the wrong things, over-rehearsing interview answers, for example, while leaving planning exercise technique or physical standards until the final weeks. A defined runway with a clear structure produces better results than an unlimited one without a plan.

As a general guide, most candidates benefit from a focused preparation period of roughly two to three months of consistent, structured work, sitting on top of longer-term groundwork like fitness and general current affairs awareness that can reasonably start earlier. This isn't a hard rule, some candidates need less, particularly if they already have relevant leadership experience, and some benefit from more, particularly second-time candidates addressing specific feedback from a previous attempt. But it's a more useful starting point than either "start now, however far out you are" or "a few weeks will do."

What Belongs in the Early Phase

Certain elements benefit from an early start regardless of how far out your assessment date is. Physical fitness is the clearest example. Building running capacity, strength, or general conditioning safely takes months, not weeks, and trying to compress this into a short window close to assessment day risks injury as much as it risks underperformance. Current affairs and service knowledge also benefit from an early, low-intensity start, reading regularly over a longer period builds genuine familiarity in a way that last-minute revision cannot replicate.

Interview preparation, similarly, benefits from starting earlier rather than later, not because you need months of rehearsal, but because knowing what to expect from OASC, AOSB, or AIB style interview questions early gives you the chance to reflect on your own experiences and identify strong examples, rather than trying to generate them under pressure close to the day.

What Belongs in the Final Weeks

Other elements are better placed closer to assessment day, once the earlier groundwork is in place. Planning exercise technique tends to sharpen quickly with focused, repeated practice and is best concentrated in the final month or so, once you understand the fundamentals and are refining pace, structure, and communication under realistic time pressure. Mock interviews and full run-throughs of the day's format also belong in the final stretch, close enough to assessment day that the experience feels current, but with enough time left to act on feedback.

Second Attempts Need a Different Timeline

If you're returning for a second attempt at OASC, AOSB, or AIB, the calendar matters less than the specific feedback from your first attempt. Rather than restarting a generic preparation timeline, the most effective use of your time is identifying exactly what held you back previously, whether that was a specific competency, a particular exercise format, or an aptitude test threshold, and building a focused plan around closing that gap. This often takes considerably less time than a first attempt, but only if it's targeted rather than a repeat of the same broad preparation.

The Real Risk of Getting the Timeline Wrong

Underpreparing is the obvious risk, but starting too early without structure carries a real cost too: burnout, stale answers, and losing the sense of readiness that comes from focused, recent practice. The candidates who perform best on the day tend to be the ones whose preparation built steadily toward a peak, rather than those who prepared the longest in total. Knowing roughly how far out you are and working backwards from assessment day, rather than starting an open-ended process, is what makes preparation time actually count.

MAP works with candidates at every stage of this timeline, from early groundwork through to final mock interviews and planning exercise refinement, and can help you build a preparation plan that fits the time you actually have rather than an idealised one.

Book a coaching session or download the Planning Exercise Guide to see how we can help you prepare.