I just graduated in May as well, and am starting work in November. I thought the same thing.. 18 months seems hard. But then, the company I'm with encourages us to finish withing 8 months of graduation (which is January). Haha now 18 months sounds great to me.
Everyone has a different technique that works for them, and everyone has different restraints on their schedules so I think this answer is different for everyone.
Anyways, in my opinionm I would say to schedule FAR & REG (they have the most material to study) for the first month of a testing window (october, january, april, or july) because you get the whole month before it to study because there are no exams. Then schedule BEC & AUD for the second month of a window (november, february, may, august).. This way, if you pass them all, you finished in 6 months. If not, there is plenty of time from the first test you passed. I'm scheduling them at the end of the month so I get the most time out of the month
So it'd be like: (example)
End of July – REG – study all june and until your test in july. (7-8 weeks)
End of Aug – AUD – study whats left of july, and until your test in august (4-5 weeks)
End of Oct – FAR – study all september, until your test in october. (7-8 weeks)
End of Nov – BEC – study whats left of october, and until your test in november. (4-5)
-Then, say you pass your first test in July, then you have until January of the next year, which gives you like at least 7 more windows to re-take any exams you failed, and plenty of time to re-focus.
That is similar to my plan.. not the order of the exams.. but the concept of it. I'm just trying to take them as close as possible but with enough room to study for that particular exam, and then if I fail any (which i did.. BEC), there is plenty of time before any expire. Some people say they can take two different exams in the same month.. but this seems to make the most sense for me. I'm sure people will agree or disagree with me, but everyone is different. Figure out a study pattern that works the best for you.
Sorry for writing a book. haha