Often when working intensely on a large project which spans over days I forget to mark the start and finish time for each session. When billing clients for time this can create problems. I thought the perfect solution to this problem would be to sort catalog by edit time, and then by view the time stamps. I could then find the first and and last edit for a session and quickly translate to session time. The only problem is I cannot find a place with LT displays this information.
It seems to be an oversight in LR -- the metadata field "lastEditTime" is available to plugins via the Lightroom SDK, but you can't use that field to define a custom tagset for displaying in the right-hand-side Metadata panel.
However, here's a workaround that might work for you: In the right-hand Metadata panel, select the "EXIF and IPTC" preset, and the field Metadata Date will show the date/time of the last time LR wrote metadata back to the file. In Catalog Settings > Metadata, make sure "Automatically write changes into XMP" is checked. This will cause LR to write develop settings or metadata changes (keywords, captions, ratings, etc.) back to the file soon after you make the changes ("soon after" is typically less than a minute).