As with the ole idea, this could as well live outside (non-embedded) of the app, to visualize a range of dates of several employees for example, or customers/visits (housecalls), no dates mind you.
Perhaps it's worthwhile to be able to switch cells from dates to days in between, so that one can visualize relevant difference in three ways.
Perhaps the dates ranges has to be selected in the spreadsheet document, to be visualized in the stand-alone app.
OOo come on over!
Hopefully the image attachment works..