Some coding suggestions:

- use /var instead of /set vor local variables, you can use short names too then
- goto is evil
- I'm a fan of regex, can't help it:

if (!$regex($1-,/^\s*(?:(\d+)wks?|())\s*(?:(\d+)days?|())\s*(?:(\d+)hrs?|())\s*(?:(\d+)mins?|())\s*(?:(\d+)secs?|()))) return
var %weeks = $regml(1), %days = $regml(2), %hours = $regml(3)
var %minutes = $regml(4), %seconds = $regml(5), %totaldays = $calc(%weeks * 7 + %days)

- how about
if ($istok(%currentmonth,4.6.9.11,46)) var %monthdays = 30
instead of 6 different tests?

- are you sure you need that _ to space conversion?