I got an email having this, Attached is the new seating chart. We’ll talk about it at the 9:00.
Is it correct?
I would replace the first the with a and get rid of the second one.
It's fine as it is. You could use "a" for the first one, but "the" is fine. There is a particular chart, so "the" is OK.
The second "the" is necessary, too. There is a word "missing" from the end. "The 9:00" refers to "the 9:00 meeting." Or "conference call." Or "appointment." Or similar.
Saying you will talk about at 9:00 is OK, but means something slightly different.