Assuming $6 is where the "Jun" of the date begins, you need more than 4 tokens to get the whole date, unless nickserv's timestamp is in the same timezone that you're in. Since they give you the 'ago' time, I'd use that instead. The 1st line takes the last 4 tokens of the notice.
var %a $gettok($1-,-4-,32)
var %a $remove(%a,$chr(40),$chr(41))
var %ago_time $duration(%a)
var %wait_until $calc(86400*7 - %ago_time)
