Only pops if the placeholder Leshy is left up. Leshy drop nothing that cannot be gained from other treants.
The NQ NM is Colorful Leshy and drops Harvest Earing. If left up long enough (assumed 24 hrs) it will change to the HQ NM "Defoliate Leshy", which in addition to having a higher drop rate can also drop a Heims Earing (the same one you can get from assault).
Colorful Leshy can take up to 24hrs to pop (has been seen sooner), but if the placeholder is disturbed in any way the timer will reset. You cannot damage or even agro it, it WILL reset the pop timer.
Edited, Mar 17th 2009 3:43pm by thatdamnelf
After catching it multiple times I've found it can spawn as early as 6 hours from time of last death, but thats very very very unlikely, usually pops between 12 and 16hrs from last kill.
Edited, Jun 5th 2009 9:15am by thatdamnelf