I gave myself a 3 month period to study, then scheduled it a month in advance. I (and I think a lot of other people) panicked the week before the test thinking that I wasn't ready. I'm glad I didn't postpone the test though, good luck!
thanks for all your replies! I wasnt sure if there were set dates to take the OATs (like how it was for the SATs). Now I just have to decide on a date...