In June 2012 the NTSB released this Safety Alert about the actual age of "in cockpit" radar weather displays such as those received by satellite services or through FIS-B. This was later revised December 2015. This is the first time the FAA or NTSB has issued any guidance to pilots on the use of satellite-delivered weather products despite the fact that these systems have been around for the better part of a decade.
They are correct in saying that the date-time presented to the user is based on the time the data was broadcast (prepared) and does not represent the actual age of the product. In this statement, they suggest that the data could be as old as 20 minutes. However, I think this is a gross overstatement for datalink products from providers such as SiriusXM and WxWorx and for the free FIS-B ground-based system. On a visit to their Huntsville, Alabama office, I've spoken directly to the technical staff at WxWorx which supplies the data for the XM-delivered satellite weather mosaic. While they do agree the actual presentation is older than the date-time stamp on the product, it should not be any older than 10 minutes at the worst case during convective outbreaks. I've explained this numerous times, but I'll repeat it below.
There are 3 potential areas of latency...
(1) The volume scan of the individual radars