I seem to recall the same thing. If the engine is warm enough to idle smoothly, you can take off. No need to warm up into the green band.
It should not be too hard to google for the operations manual for the engine as written by the engine manufacturer - on which the AFM of the aircraft will be based. Is there any information about this issue in there?
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Edited:
http://www.7ts0.com/manuals/lycoming...TIO-360_OM.pdf
Page 3-5:
) Engine is warm enough for take-off when the throttle can be opened without the engine faltering.