Something

/m {
if ($1) {
   set %temp
   %temp = 60 * $1
   /mode #lurk +m
   msg #lurk $me has set the channel on +m for $1 minutes; Reason: $2-
   .timer 1 %temp /mode #lurk -m
   unset %temp
}
else {
   /mode #lurk +m
   msg #lurk $me has set the channel on +m for 10 minutes.
   .timer 1 600 /mode #lurk -m
}
}