diff --git a/.github/workflows/ci_test_cleanup.yml b/.github/workflows/ci_test_cleanup.yml
index 3f7252123..a3fe6512d 100644
--- a/.github/workflows/ci_test_cleanup.yml
+++ b/.github/workflows/ci_test_cleanup.yml
@@ -48,7 +48,7 @@ jobs:
       # The additional 10 minutes is just to be good citizens.
       - name: Set purge boundary
         run: |
-          echo "HALF_HOUR_AGO=$(date -u -v-30M --iso-8601=seconds)" >> $GITHUB_ENV
+          echo "HALF_HOUR_AGO=$(date -d '30 minutes ago' -u +"%Y-%m-%dT%H:%M:%SZ")" >> $GITHUB_ENV
           echo "set half hour ago to: ${{ env.HALF_HOUR_AGO }}"
 
       # run the folder purge