diff --git a/scripts/ops/hermes_demo_lib.sh b/scripts/ops/hermes_demo_lib.sh
index df42864d7..468a3dfde 100644
--- a/scripts/ops/hermes_demo_lib.sh
+++ b/scripts/ops/hermes_demo_lib.sh
@@ -67,11 +67,17 @@ last_build_number() {
     python3 -c 'import json,sys; print(json.load(sys.stdin)["lastBuild"]["number"])'
 }
 
-wait_for_build() { # job number [tries] -> prints result
-  local job="$1" num="$2" tries="${3:-120}"
-  for _ in $(seq 1 "$tries"); do
-    sleep 10
-    local body result building
+# Polls before sleeping, not after. Sleeping first meant a build that had
+# already finished still cost a full interval of silence, which on stage reads
+# as the script having missed it. The interval is short for the same reason:
+# the wait is dead air in front of an audience, and a Jenkins status read is
+# cheap.
+BUILD_POLL_SECONDS="${BUILD_POLL_SECONDS:-3}"
+
+wait_for_build() { # job number [max_seconds] -> prints result
+  local job="$1" num="$2" budget="${3:-1500}"
+  local waited=0 body building result
+  while [ "$waited" -le "$budget" ]; do
     body="$(jenkins_get "/job/$job/$num/api/json?tree=result,building" || true)"
     building="$(printf '%s' "$body" |
       python3 -c 'import json,sys; print(json.load(sys.stdin).get("building"))' 2>/dev/null || echo unknown)"
@@ -80,6 +86,8 @@ wait_for_build() { # job number [tries] -> prints result
       printf '%s' "$result"
       return 0
     fi
+    sleep "$BUILD_POLL_SECONDS"
+    waited=$((waited + BUILD_POLL_SECONDS))
   done
   printf 'TIMEOUT'
 }