While browsing categories in list mode, there’s a clock icon under each track’s waveform that indicates the duration of the preview. But the length of the preview does not really mean anything, as we place different versions of a track back to back in the preview. So for a track with different versions, one could end up with a 10-minute preview, whereas the track itself is just a couple of minutes.
I think that bit of information would be more relevant if it indicated the main track length, maybe followed by three dots to indicate that more versions are available.