Turns out AWS is very persistent about delivering your push notifications!  If the mobile endpoint is not available, SNS will retry 2 times immediately, 5 times at 20 seconds apart, then 31 times exponentially backing off from 20 seconds to 20 minutes and finally 12 times every 20 minutes for a total 50 attempts over more than 4 hours before the message is discarded from SNS.  Damn!