create a service file:
cp /lib/systemd/system/crond.service /lib/systemd/system/sleep.service
vi /lib/systemd/system/sleep.service
create a script to be executed
vi /usr/sbin/sleep.sh
#!/usr/bin/bash
sleep 1000
make the script executable
chmod +x /usr/sbin/sleep.sh
enable the service
systemctl enable sleep.service
start the service
systemctl start sleep.service
check status
systemctl status sleep.service