var %variable $calc($insong.length / 1000)[/code[
shouldnt it be

var %variable = $calc($insong.length / 1000)

and is the halt necessary? cant u do

alias inlength {
if ($inmp3) {
var %variable $calc($insong.length / 1000)
return $gmt(%variable,nn:ss)
}
}

i may be wrong, so feel free to correct me

otherwise, i havent tested it, but it looks like it would work great, good job