Thanks! I actually figured out a solution like this:

$uptime=$snmp->get("sysUpTime.0");
$uptime=localtime(time()-($uptime/100));
[download]

For an "upsince" stamp...
However, I like the granularity of your solution, so I think I'll plagiarize the heck out if it if you don't mind, as it'll give me a better timestamp for the HTML output.. Thanks!