If you start from the Syabrubesy village (1420 m) :
Lamtang is a narrow valley (Bhote Kosi or “river from Tibet”) in the south of the Tibetan border and the Nepal. The Lamtang Lirung (7246 m) in the north and the Dorje Lakpa(6975 m) at east are the border with Tibet ( or China).
It’s a smal isolated region who are habitated by by people from Tibetan origin( Sherpas) . “Lam” is the tibetan traduction for yack and “tang” or “dang” mean the way … So you’ll follow a way for yack. Syabrubesi (1420 m) is last stop before the China border. It’s only at 75 km from Katmandu by road. Slowly, in 4 days, more or less you can walk the way (20 km). The difference of altitude between Kyanjin Gumba (3830m) and Syabrubesi is only (2410 m). All the way you will find excellent accommodations , shops and tea or coffee houses were it’s possible to eat or drink ( each 2 km ). Most of the time, the way following the river is inside a very nice damp forests and alive with birdlife always . Above (2400 m) slowly the forest is less dense with large pines and drier. After the valley is more and more large and the way is more and more easy. In this National Lamtang Park, in that valley , you will see (if you are lucky) many free animals as musk deer and Himalayan tahr, red panda, Himalayan black bear, snow leopard, ghoral, monkeys, birds, yacks …Kyanjin Gumba (3830m) is the last village occupated of this fabulous Lamtang valley. There is the famous Lamtang yack cheese factory. There is also a small Budhist monastory.
The timing : It depend of your physical condition and the time you want to stay.