Hi, there’s an important thing to know: Center Duration is based on whatever TC you are tracking in the top line above the Record monitor.
For 23.976p projects, timecode is, and should normally be TC24 (there is no 24DF timecode standard in the world today). This means that the timecode will not match real “earth time”.
A workaround for that is to switch your Master timecode from TC1 or TC24 to 30DF, since Avid allows you to track most any form of timecode standard. This would mean you do get an actual earth time center duration.
Reading your issue with being a few frames off, you might have the Master TC above the record monitor set to something else. Switching it to TC24 should at least give you a center duration that matches that TC counter.