Dimitri Bologna, might be this:
QueryPropertyHistory returns a data set created by querying each logged property on a thing and then combining the individual datasets into one big data set. A "row" is created for each time stamp in the individual data sets. If there is a logged value with that time stamp, it is entered in the row of the data set. If there is no logged value, the last logged value for that property is used. If there is no logged property; the entry is left blank.
Many Thanks Sbalta.
Ok, If I well understood how the service QueryPropertyHistory works, the problem seems to be the data packet storing into the server.
I need to understand why the row into db are written with the same server timestamp while I sent that the packets with different client timestamp (30 sec between).
Could this be due to the short time between the packets , 30 seconds delay?