Didn't know you could get the NG without autothrottle.
Anyway, I've flown -800's on 10 minute sectors as well as 5 hour sectors. 90% of the time we use VNAV or LVL CHG from TOD, so the autothrottle will retard to idle from the very start.
Again, no problems.
If operating with manual throttles I don't really think you would retard the throttles any faster than the autothrottle rate. This would be very uncomfortable in the back. Then again, I have met plenty of pilots who have "seen the light", and operate according to logic understood only by themselves.
Nothing is impossible.