Little known fact about the possession stat in soccer - it's nothing more than a percent of total passes, so the two stats you're talking about are identical
Fans understandable assume its a measure of time of possession, and to be honest I don't know why stat companies don't do it that way. I know from working briefly for Opta that they mark when possession changes, it wouldn't be hard to make some calculations based on time of possession.
I was today years old when I learned this.