You can set the value of %var to 5 times what you want, then when it decrements, only take action if its a factor of 5.
For your specific need, I dont really understand how you were going to use that, you cant set that off then loop waiting for it to decrease, becuase it only decreases when your script ends.
This should work for your need...
alias whoisem {
var %i = 0
while ($0) {
.timer 1 %i whois $1
inc %i 5
tokenize 32 $2-
}
}
just sets off a bunch of timers to do the whois job.