[15 mins to wdw]

well that is true about the time printed on the fastpass when another will be availble, generally you will be on the ride about that time anyhow. however you might be able to go and get another fastpass then do the orginal fastpass ride.

and yes it is possible to run out of fastpasses, for example on christmas day they ran out of fastpasses at 11am for test track and the park was open till 9:30 that night. although that park was packed that day.