Same day FOP Fast Passes were very hard to come by during the first week of June last year. Navi was even more difficult.
Fortunately, the standby line for FOP would get down to about 20 minutes just before closing time, with Navi even shorter. Another good time to visit Pandora is when the first showing of Rivers of Light is underway.
Just keep in mind that the posted wait times are intentionally exaggerated at night to discourage late riders. That 20 minute wait could be posted as 80-100.
When in doubt just ask the attendant. They do know the actual wait.