The confusion may exist between the requirements for the first (international) flight and every other flight.

When your OWE ticket is issued (that is, when you pay for it and either a TA or airline writes the ticket), you must have a reservation for your first international flight. You have to make this reservation and buy the ticket a minimum amount of time before the first flight -- that minimum amt of time is anywhere from 1 hour to 22 days, depending on class of service and place where the ticket is issued. You can't change this first flight without incurring a penalty. In addition to reserving a specific first flight, your ticket must also set out the full routing that you will take -- that is, a list of all the flight segments in your OWE.

For each segment after the 1st (int'l) flight, you can choose either to have a confirmed reservation or to leave the segment "open." Open means that the flight segment is part of your OWE ticket, but that you have neither a reservation nor a specific date for the flight segment.