I tend to drive off more or less straight away, as mine is a little grumpy when cold so I like to get her to temp briskly without abusing her - If you drive off normally straight away without too many revs or labouring the old girl, the oil pressure will be higher than at idle and consequently better for the engine.

When returning i've usually been giving her a jolly good thrashing so tend to take the long way home or go round the block a bit, off boost and with the heater on full to dissipate some heat and get the turbo slowed down before I put her to bed.

The thought of switching the engine off immediately after a hard run and leaving my lovely turbo spinning wildly with no lubrication makes me shudder, as would the idea of letting her gently cook herself and her oil by just stopping and turning off without a cooling down period.

To summarise, keep up the good work, but don't worry about letting her idle at cold for too long - you could be doing more harm than good - 30 seconds or so should do it.