While I never want to say anything is a sure thing, I think a lot of people underestimate what they could do if they commit 6 months, give or take, to the goal. I won’t even get into underestimations of potential if one would be willing to commit for years because that’s not your question. The problem is that most people don’t know what they could do so they never commit that kind of time to it. Is a 9-12 minute improvement possible? Sure it is if you commit to it for the next 6 months. Is it likely? Only time will tell.
As for training, with the marathon, the first thing is run as much as possible. I remember Double saying frequently that he thinks it’s important to get out for some kind of run every day, even if it’s a 2-3 mile run. If you get out the door every day, your weekly mileage won’t suffer too badly no matter what happens. Beyond that, I’d focus on strength and stamina. I’d work hills into regular daily runs every day or at least almost every day if at all possible. As you get into the final few months, I’d suggest focusing on long (at least 30-40 minute) tempo runs and long repeats like 1-2 mile repeats with short recoveries. Given time limitations, I’d probably stick with fartlek workouts for turnover rather than hitting the track, which can quickly eat up a lot of time. Of course, these are just general ideas.
What did your training look like last year? It’s hard to say what kind of training one would envision it taking to accomplish any goal but it’s that much harder without knowing what kind of training resulted in previous accomplishments.