Hi Rob, I would never take the GT out for less than 20 miles - it's probably a hang up from all the V12's I've owned. Gets them warmed up and drys out any condensation formed in the exhaust systems. On most occassions I would check the oil - I like doing it, gives me a chance to check the engine for any leaks on the GT too!
Getting the oil up to temperature is, I guess, what Ford need you to do with the GT before checking the oil. There has been much debate over the years (before the GT arrived) about when to check the oil in engines - on the V12's I'd always check cold as the oil would have dropped right the way through the engine to it's 'absolute' level. If warm, oil would still be dripping through.
The GT is clearly different as it has a dry sump and it seems to require it measured warm.