It's not cryptic at all. The alias does stuff every <random> seconds. The first thing it does is set a timer so it will do something in the future. You can have the timer created as the last thing, if you want, as long as it gets created. If you want it to say 'hello' at a random interval between 15 to 20 minutes, which is 900 to 1200 seconds, you can have the alias be like:
alias dostuff {
msg #channelname hello #channelname
timerDoStuff 1 $rand(900,1200) dostuff
}
