Run task every 90 minutes with cron

Question

Trying to adjust a cron job to run every 90 min. It was previously running every 20 min, which was a simple cron job:

*/20 * * * * whatever

To change it to every 90, it seems like I need to split it into 2 jobs, I've done this:

0 0,3,6,9 * * * whatever
30 1,4,7,10 * * * whatever

Is this right? The job doesn't seem to kick off.

Answer 1

That should work, except that you need:

0 0-21/3 * * * whatever
30 1-22/3 * * * whatever

24 hour time :)

Answer 2

try this.

how-can-i-set-cron-to-run-certain-commands-every-one-and-a-half-hours