I'd hardly consider an extra 6 minutes anything to get your knickers in a twist about.
Scuzi - it might be the difference between binning your alternate and committing (shock horror) to LHR.
In level flight on the Scarebus 6 mins is a tad over 200kgs of fuel. An approach into LHR from the stacks about 400-600kgs.
On a fair weather day (if there is such a thing any more) we aren't always awash with gas. Hence my point that the sooner we know an accurate figure (if poss) the better.
Cheers
SD