diff --git a/release-hold/action.yml b/release-hold/action.yml
index ccc154d..a6b79f6 100644
--- a/release-hold/action.yml
+++ b/release-hold/action.yml
@@ -56,6 +56,7 @@ runs:
         REPO: ${{ inputs.repository }}
         GITHUB_REF_NAME: ${{ github.ref_name }}
         GITHUB_REF_TYPE: ${{ github.ref_type }}
+        GH_TOKEN: ${{ github.token }}
       run: |
         set -euo pipefail
 
@@ -147,8 +148,20 @@ runs:
             ;;
         esac
 
-        # Calculate age
-        ANCHOR_EPOCH=$(date -d "$TIMESTAMP" +%s)
+        # Parse ISO-8601 timestamps portably across GitHub-hosted runners.
+        PYTHON_BIN="${PYTHON_BIN:-}"
+        if [ -z "$PYTHON_BIN" ]; then
+          if command -v python3 >/dev/null 2>&1; then
+            PYTHON_BIN=python3
+          elif command -v python >/dev/null 2>&1; then
+            PYTHON_BIN=python
+          else
+            echo "❌ Error: python3 or python is required to parse timestamps"
+            exit 1
+          fi
+        fi
+
+        ANCHOR_EPOCH=$("$PYTHON_BIN" -c 'import datetime, sys; print(int(datetime.datetime.fromisoformat(sys.argv[1].replace("Z", "+00:00")).timestamp()))' "$TIMESTAMP")
         NOW_EPOCH=$(date +%s)
         AGE_MINUTES=$(( (NOW_EPOCH - ANCHOR_EPOCH) / 60 ))