Delayed Entries - which field does the Period day filter use

Hi all,
I try to request all tracking details for the last day. The request looks like e.g.:

I run this request @02:00 AM
When I run the same request e.g. at 02:00 PM, I received more details…

I guess, that this should be caused by the interpretation of the date!?
->Against which field is the date checked? firstAction or LastAction date?

Or is it possible, that the processing of the 2021-06-10 details is so slow, that they are not finished at 02:00AM? If yes, where I can check if the processing is finished?

Thanks and best regards