Laurent,
You could indeed have a maximum of 10 minutes delay in the position of traffic - as the FTP upload is delayed by 5 minutes for security reasons and the Network data on your screen is already delayed by 5 minutes, so 5 + 5 = 10 minutes.
In summary, Live traffic on your screen will show as 5 minutes delayed when it appears on the FTP uploaded map and Network traffic up to 10 minutes behind where it really is.