Sweet Thanks for the quick reply.
For anybody else interested in the final code:

on *:text:!countdown:#test:{
msg $chan To start the Timer type !countdown and the time until the next notice. Exp: !countdown 50
msg $chan The Timer will then automatically countdown to that time and continue from there on in 7min intervals
msg $chan To stop the Timer type: !countdownoff

on *:text:!countdown &:#test:{
%var = $calc(420 + $2)
if (!$timer(countdown)) {
.timercountdown 1 $2 msg $chan Text
/timer1 0 %var msg $chan Text

on *:text:!countdownoff:#test:{
/timer1 off