Check for an item value if it is from today

[markfree]

I have a prototype item that basically receives a file write timestamp in unixtime which indicates its last arrival time.
Everyday a new file is created with the same name and Zabbix receives its arrival timestamp.

Now, I wanted to create a trigger that checks if there is a new file arrival time for the current date.
For now, my raw logic is something like this:
Between 00h and 02h30 there should be a new file coming, and should it not arrive, it is a delay; therefore, an event should be created.

if time() > 023000 and last(file timestamp) <> today, then trigger alarm.

I'm not sure how to create that trigger.
How should I read the date from that item (timestamp value)?

[markfree]

For now, I have tried something like this.

nodata(/host/key[{#NAME.SUFFIX}],4h)=1
and
time()>040000
and
dayofweek()>=2
and
dayofweek()<=6

But this expression does not account for "Discard unchanged" preprocessing, which my item uses.
So, it always triggers after 04h.

Any thoughts?