Thank you for your advice, it helps ! I was used to the crontab like in unix systems, with 5 fields for the period, so I was wondering... I will try it monday and tell you. Have a good we.
It works as intended. Thanks. I have now a new pb : it stopped pinging two days ago, while the windows service continued to work. I don't see the pb in the log files. I restarted the service and now it pings as expected. I will close this topic and post a new one for this pb.