Mike,
When I try to manually update your river page, I get this message:
Next update after Monday September 2nd, 2013 10:44 PM EDT
Looking at the river-config.php file, I see this line:
$TotalTime = ((4*60*60)-180); // Time of delay. *Note the -180 is to avoid missing the next run time.
// *Time listed above is 4 hours.
That equals 14,400 seconds for the 4 hours. Try changing the time in the parentheses to 900, which is 15 minutes, and see what happens.