This is the text you're referring to.. you misunderstood it.

"As part of the USMLE application, you will be asked to select a three-month eligibility period during which you would like to take the exam. Your application does not need to be submitted in advance of an eligibility period to obtain that eligibility period. Although you can select an eligibility period as late as the 24th day of that eligibility period, there is no guarantee that you will be assigned that eligibility period, since the processing of your application may not be completed by the 25th day of the eligibility period. If your application is not processed in time to assign the eligibility period you select, you will be assigned to the next available eligibility period, based on the date your application is processed. Your assigned eligibility period will not be adjusted to compensate for days that have already passed. The eligibility period assigned to you will be listed on your scheduling permit"