Delivered fuels are assumed to be used completely during the month in which they were received. The Start and End Date for the delivery are the first and last day of the month in which the delivery occurred.
For example, if you had fuel oil delivered on March 10, then March 1 would be the Start Date and March 31 would be the End Date. Months with no delivery are counted with zero consumption. Even if a delivery came on March 31, it is counted only for the month of March.