How to schedule jobs in Jenkins every 3 hours

Question

How can I schedule a Jenkins job to run every 3 hours between 0900 hours and 2100 hours every day?

I tried:

0 9-21/3 * *

but it gave me an error:

Invalid input: "0 9-21/3 * *": line 1:13: expecting space, found 'null'"

Solution

Doing this should work. 0 9-21/3 * * *

But to avoid the errors & then the warning about "spreading the load evenly" use this. H 09-12/3 * * *