Batch evaluation with a 24 hour timestamp lookback - same 24 hour period each evaluation?

Hello,

I have been struggling to conceptually understand how this scenario will play out and any insight will help. 

Scenario:

Segment evaluation method: batch (I only need to send updated audience once per day to a destination, and do not want to use up our 500 allotted streaming segments). Our batch evaluation kicks off each day at 12:30 PM UTC.

My definition states: (Include audience who have at least 1 Any event where (Business Journey Name equals XX and Channel equals All and Wave equals 1 and Event Type equals export.qualified) ) and occurs in last 24 hour(s)

I am curious how the "and occurs in the last 24 hour(s)" piece of this will function since evaluation ends at different times each day. Does the 24 hours time apply at the kick off of evaluation, the last timestamp of a successful audience evaluation, or something else? I want to ensure that I do not skip over qualified contacts if the 24 hour time period happens to change with each evaluation, or that the same contacts from the previous 24 hours time period remain in the audience on the second run if the 24 hours time period overlaps with the previous run.

My main question is: What hour/time of day does AEP reference when using a 24 hour lookback time period?

Thanks,

Hannah