Hah, I didn't realise this existed. My Garmin reckons 3 hours and 4 seconds.
So I just match my HM PB for the first half, then knock 14 minutes off it for the second half. Maybe I'll put in a little sprint on the home straight to duck under 3 hours. Simple...
lol, my garmin predicts a 2:43 marathon for me at the moment....!