Courtesy of google:

Pick the pods at the tender stage at maximum length, before the seeds mature or swell. Yard long beans may grow up to 24inch long, but it is better to pick them at 12 to 18 inches.

While picking, cut the pods with a sharp knife to minimize plant damage, thus maximizing harvest. Leave the pods to reach full maturity, allowing them to dry on plant, if the pods have to be reserved for seeds. The pods will break open and the seeds can be collected.

Native to Southeast Asia, this climbing plant is a close relative of the cowpea or black-eye pea.

A pencil-thin LEGUME that resembles a GREEN BEAN except that it can grow up to about 3 feet long (though it's usually picked at 18 inches or less). Yard-long beans belong to the same plant family as the BLACK-EYED PEA. In fact, in parts of China the bean is allowed to mature until full-fledged peas are produced in the pod. Yard-longs have a flavor similar to but not as sweet as that of a GREEN BEAN, with hints of its black-eyed-pea lineage. The texture of the pod is more pliable and not as crisp as that of a GREEN BEAN. This LEGUME, also called Chinese long bean, long bean or asparagus bean, can be found year-round (with peak season in the fall) in most Asian markets and some supermarkets with specialty produce sections. Select those that are small (which equates to younger) and very flexible; the peas should not have matured. Refrigerate in a plastic bag for up to 5 days. Yard-long beans are most often cut into 2-inch lengths and sautéed or STIR-FRIED. Overcooking will make them mushy. These beans are rich in vitamin A and contain a fair amount of vitamin C.

Maybe someone with personal experience will come along and give you more info.

Hi, This is one of my favorite veggies to grow !
Pick them when they are about 15 inches long.

cut them up..great taste , not the same as a string bean.

D`Ann

I heard these do well in the heat. I shall be planting some soon.

Well I guess I waited to long to harvest them.
Oh well, they still look really neat and I will have plenty of seeds to plant.