What is a billing cycle?
The stretch of days a dairy settles in one go — ten days in much of north India, where it is called a dashak.
Dairies do not settle daily. They collect for a stretch, then pay everything at once. Ten days is the commonest in north India and is called a dashak; fifteen days and a full month are also widespread.
The cycle decides more than the bill. Payments are tagged to a cycle, dues are carried between cycles, and the report you open defaults to the cycle you are in.
One detail worth knowing in Dairywala: cycles are anchored to the month rather than rolling. A length of 1 to 27 days cuts fixed blocks starting from the first of the month with one shorter block at the end, and choosing 30 gives you a full calendar month rather than a rolling thirty days.