I originally took up SBR but then I found out that there are no appointments for it available in my area. So I thought that I could prepare for an Option exam instead, and APM is one I already plan on taking. Do you recommend preparing for it in a month?
It depends on hom much time you have available in the month. Eg, are you working during the day leaving only evenings and weekends for study? If you can study full time you could prepare in a month.
The most important part of your study is question practice. Do not spend too long reading a study text. Instead, practice questions.