Hey, the process of taking STEP 1 if you are Foreign Medical Graduate is linked with ECFMG, you must first register with them, then you register for the exam through their service.
At this time you are required to choose a 3 month validity period, meaning you lock down a a set of 3 months during the course of the year in which you plan on taking the exam...the 3 months are in sequence-for example I chose a "December, January, February" Block
The date selection is based on the next step....when you receive your Examination Permit a certain Prometric scheduling number will be given.
Next you must go to the Prometric website, (there will be detailed instructions on your permit) choose your testing location and check for Available Dates
The availability of dates will be based on the Prometric Center
SO before you begin this process be confident at the General time of the year you plan to take it. But before you choose the date make sure you are confident, by testing and re-testing yourself with NMBE's - Question Banks etc....