diff --git a/Dockerfile b/Dockerfile
index 5e983bf..4fe1f0f 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -2,6 +2,13 @@ FROM debian:stable-slim
 
 ENV DEBIAN_FRONTEND=noninteractive
 
+# Default is to run cron job in the 10th minute of each hour
+# You can override at runtime with -e CRON_MINUTE=xx
+ENV CRON_MINUTE=10
+# Default port for http server inside container.
+# You can override at runtime with -e PORT=xxxx
+ENV PORT=8080
+
 # Install required packages: curl, cron, busybox (httpd), ca-certificates
 RUN apt-get update \
 	&& apt-get install -y --no-install-recommends curl cron busybox ca-certificates gnupg dirmngr \
@@ -25,14 +32,8 @@ COPY start.sh /usr/local/bin/start.sh
 # Ensure scripts are executable
 RUN chmod +x /usr/local/bin/run_speed_test.sh /usr/local/bin/start.sh
 
-# Add cron job to run every hour at minute 0
-RUN printf "0 * * * * root /usr/local/bin/run_speed_test.sh >> /var/log/cron.log 2>&1\n" > /etc/cron.d/speedtest-cron \
-	&& chmod 0644 /etc/cron.d/speedtest-cron
-
 # Expose default HTTP port and declare data volume
 VOLUME ["/var/www/data/speed"]
-# Default port for http server inside container. You can override at runtime with -e PORT=xxxx
-ENV PORT=8080
 EXPOSE 8080
 
 # Start script will launch cron and the HTTP server
diff --git a/start.sh b/start.sh
index 1aff8a8..b6fb8b0 100644
--- a/start.sh
+++ b/start.sh
@@ -2,6 +2,9 @@
 
 set -e
 
+CRON_MINUTE=${CRON_MINUTE:-10}
+PORT=${PORT:-8080}
+
 # Ensure data directory exists
 mkdir -p /var/www/data/speed
 
@@ -17,20 +20,17 @@ chmod -R a+rwX /var/www/data || true
 # We run it in background so server starts promptly. The cron will run hourly.
 /usr/local/bin/run_speed_test.sh || true &
 
-# Ensure the cron job exists in root's crontab (so `crontab -l` shows it)
-CRON_ENTRY="* * * * * /usr/local/bin/run_speed_test.sh >> /var/log/cron.log 2>&1"
-if crontab -l 2>/dev/null | grep -F "$CRON_ENTRY" >/dev/null 2>&1; then
-	echo "cron entry already present"
+# Ensure the cron job exists in Cron
+CRON_FILE=/etc/cron.d/speedtest-cron
+if grep run_speed_test ${CRON_FILE}; then
+    echo "cron entry already present"
 else
-	(crontab -l 2>/dev/null; echo "$CRON_ENTRY") | crontab -
-	echo "installed cron entry into root crontab"
+    echo ${CRON_MINUTE} '* * * * /usr/local/bin/run_speed_test.sh >> /var/log/cron.log 2>&1' > ${CRON_FILE}
 fi
 
 # Start Debian cron in background
 service cron start || cron || true
 
-PORT=${PORT:-8080}
-
 # Start busybox httpd serving /var/www on configured port in foreground
 if command -v busybox >/dev/null 2>&1; then
     echo "starting busybox httpd on port ${PORT} serving /var/www"