Anything can be milked once a day / twice a day. Heck, milk em 3 times a day (but that'd be straining on the animal....)
Milk as much as you need - don't need much milk, only milk once a day. Need more / only have a couple animals, milk twice.
They produce as much as being taken. Our goat gave us a gallon a day because her year old wether decided to milk her when her 8 week old kids were still milking. Well, the wether started milking her after she gave birth until we sold him, then she never weaned her kids. So when we sold them at like 9 weeks we started milking her because she had a gallon a day.
Anywho, just wanted to add that in ^^
