ooookkkkk. These 6 replies mimic the debate between my flight examiner and me. He has heard it is due to MRG temp rise due to inadequate lubrication, therefore if you are in a hurry you can fly takeoff power for 5 minutes, back off for a minute to "get the oil back between the gear teeth", then jack the power back up for another 5 minutes, rinse and repeat.
I'm pretty sure its due to derated HP for 2200 TBO. And if they'd meant "intermittent speed enhancement power" they'd have said that in the POH.
If I can get somebody at Robinson to answer the phone, I'll post their answer.