Confusion on Statistic Card Period Attribute

Dear HA Community,

I am a bit confused on the Period attribute in the Statistic Card. When exactly does ‘day’ begin? 0:00 of the current day or does it cover the last 24 hours ?
Same for year, ist it the last 365 days or starting at 1.1.202x.?

What I am looking for is static values for the current day starting at 0:00 and the last 365 days.

It’s a calendar period, ie, 1 day is from 0:00:00 - 23:59:59.

But it also supports a fixed period of arbitrary duration.