Using COUNTIF to counter number of times X appears in list

Depends on the format of the column of "dates". Are they text or actual date&time values?

If the values in B are text and E1 has the text (not date & time value) Feb 22, 2023

=COUNTIF(B,E$1&"*")

If the values in B are date&time values and E1 has the date & time value 2/22/23 formatted any way you like to see it presented and was entered into the cell without any time (so it's value will be 2/22/23 12:00AM)

=COUNTIFS(B,">="&E$1,B,"<"&(E$1+1))

You might try something like this:

Add a column to your data table with a formula like this:

In the new column where column A contains the ISO message time:

=TEXTBEFORE(A2,"T")+"0m"

(the +"0m" coerces the text to a Date & Time value)

Then you can use COUNTIF like this:

=COUNTIF(Data::E,A2)

Change E to whatever column you have for the added column.

Or don't bother with a COUNTIF formula at all! Just use a Pivot Table, and get your answer with a few clicks and drags.

Click the data table and from the menu choose Organize > Create Pivot Table > On Current Sheet.

Then in the Pivot Options pane drag the Fields down into the boxes below as follows:

SG

Edit:

If the values in B are text and E1 has Feb 22, 2023

=COUNTIF(B,E$1&"*")

If the values in B are date & time values and you did not create a custom format that added EST to the end, I'm not sure what the second formula will do. Numbers does not have a built-in format that includes the time zone. It might adjust them to GST before it does the comparison.