Bivouac in the rocks about halfway up from Chhukung village to Kongma La saddle on the Three Passes trek, or at the ascent to Kongma Tso (Mehra Peak). The bivouac is located on the first terrace of the valley above the moraine traverse of the Nuptse Glacier. There is plenty of space around to pitch tents on the grassy plain. Great morning views of Ama Dablam, from the slopes above the bivouac you can see the glaciers above Imja Tsho and in good weather, Makalu.
The spring is just up the trail to Kongma La.
Probably anytime...
Follow the trail to Kongma La, the bivouac is in the rocks above the ascent to the first floor of the valley, just below the place where High Camp is marked on the maps. From the bivouac it is only about 2 hours to the saddle.