Yes, the application process doesn't give you much time to establish yourself academically if you are doing a one year course. However, now you know that, you just have to make best effort to hit the ground running as it where, make a good impression. Also, because you are a mature student, the admissions staff will look much more closely at what you have been doing work/experience wise. So your application should focus on what you have been doing between leaving school and this application and how it supports your academic aspirations. So any work/experiences where you have had to produce reports, analyse information, meet deadlines, make arguments for a case, read a lot etc are taken as equivalent to the skills gained in sixth form study.
Not sure that's a very clear explanation, but what I'm trying to say is that the fact you have only one month on the academic course doesn't really matter, that's not what the decision to make an offer will be based on.