Did you try the !uptime trigger from the same mirc you have the script loaded on? It will only work when someone else types it.

If you add this to the script it will respond when you type the command.

Code:
on *:input:*: if (!$ctrlenter) && (!$inpaste) && ($left($1,1) != $readini(mirc.ini,text,commandchar) || $1 != /msg || $1 != /me) && ($1 == !uptime) tuptime

http://scripting.pball.win
My personal site with some scripts I've released.