In general, 6 mos is seen by most to be the minimum program length to get approved. It seems, even though I have not read in this group but others have, some have gotten approved with one month. So I guess the questions you have to ask yourself are: Do I go try to get by with a one month course and increase my chance of getting rejected (and losing my application fee) or do I go with what is generally seen as the minimum course length and increase my chances of getting approved?

As the Thai ladies like to say, "Up to you."