I would suggest that you just zoom in with Nutcracker to add the detailed timing marks.
Audacity will let you put a timing mark anywhere. Nutcracker is going to move that timing mark to the closest 25,50 or 100ms when you import the mark anyhow.
Just keep double-clicking the wave form at the top in Nutcracker and it will keep zooming in until you've got plenty of detail for precision.
-Steve