The default value of Timeout is 1000000 nanoseconde (1 sec) and the retrie is 5 thsi value is set by Net-SNMP library.
#!/usr/local/bin/php
<?php
$time_start = microtime(true);
$reponse = snmpget('10.5.1.1', 'public', "1.3.6.1.2.1.1.3.0",1000000,5);
$time_end = microtime(true);
$time = $time_end - $time_start;
echo "Delay in $time secondes\n";
?>