You might want to be careful with that because sometimes the date field gets filled with when the book was posted to a site rather then the date entered into Calibre. For example, I just downloaded
Kevis Hendricksons Gaia trilogy and loaded it into Calibre. The date field was filled in and defaulted to when the book was posted to Smashwords. I had to manually change the date to today.
Just an FYI.