I would start by dropping the notion that there are a set number of hours required to prepare for this exam. Everyone is different, so there is absolutely no way to answer your generic question. Do 1000 passages and then you'll be ready. Thoroughly go over every question you miss and/or are uncertain of and then you'll be ready. Do enough practice FLs from good sources and then you'll be ready. Know conceptual material fairly well and be excellent at solving multiple-choice questions about its applications to many different systems, then you'll be ready.
Good luck!