As a professional engineer, but unfamiliar with the "detail" of aircraft installations, the 7/8 secs is in my view highly relevant
At first sight the 7 or 8 seconds difference could have been explained by a single fuel source going through a fuel crossfeed valve ...
I believe that kind of engine must be around 1000kg/H at ground idle, so flight idle would not be far from 1 Liter every 2 seconds