[twinkletwinkle_]

It's not "impossible", just not natively obvious. The solution I remember using is

    0 * * * * foo()
    0 * * * * sleep 30; foo()

It's not the prettiest but is a reasonable imitation of a 30 second cron.

[xtracto]

You got it! the main idea is for it to be a "solve the problem" thing with certain framework.

I've got guys that just google it, others that do a script and sleep within the script, and the guy that suggested the while. All of them are "right" answers for me... I don't really care about how they do it, but the process perform while doing it.

Fact is, during the life of a DevOps, they will need to solve things that they don't know how to, so they'll need to be able to at least Google-fu themselves out of the problem.