A day schema specifies whether or not the individual hours of the day should be considered during the aggregation of minute, quarter hour, or hour values to day values. In this way, you can ensure that only values for a particular time of day are used when calculating the daily average values.
Create your own day schema if you want to ensure that only certain hours of the day are used during aggregation. You can also use a calendar schema to assign different day schemata to different days. In this way, you can, for example, use different periods from Monday to Friday as on Saturday and Sunday.