Well there must be some wisdom in boeing saying that you need to put the start lever to idle at 25% or they would have mentioned to wait till the N2 reached max motoring(which is only if it doesnt reach 25%).
as far as max motoring goes, as it says, it is the stage whn ur N2 has reached an almost constant figure(<1% change in 5 secs)
Even I have encountered some capts who wait for increased motoring(some saying they want to decrease the EGT) i guess its their own personal procedure so better to check with them
Cheers!