Greetings from one of your friendly SIG Testing leads!
prowjob definitions in kubernetes/test-infra/config/jobs are auto-bumped to use their latest image at 8:30am PDT and 1:30pm PDT Monday - Friday
As of last week, we're using the same mechanism to automatically bump the images used in prowjob definitions. The schedule is staggered from prow and prow build cluster auto deployments to make it easier to track down what changed for jobs that take >60min to run (e.g. many of our release-blocking jobs)