I also let it idle no more than 30-45 secs or so, usually until the rpm's start to drop. This usually coincides with the SAP turning off. Just let the oil start to flow.
Also, the ATF does not get warmed up by idling. It warms up from the engine, so driving gently until the temp needle starts creeping past 10 o'clock is the best way of warming the car up (in my books).

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Stable: e92is, e46 M54B25, e83 N52, e53 N62 - sold, e39 M54B30 R.I.P.