I found one inconsistency at Date Ranges at Planning Box (specially at Rounding dates during editions) but the same problem can be happens for other parts, specially considering tasks.

When I define in one task:

start_date: 2008/01/01 stop_date: 2008/01/02

that means that one task should be done at 01/01 at 01/02, or 2 days. I'm considering that the stop date is also a part range of task and we don't use hours at tasks yet, so if we try to get the date range:

stop_date - start_date = 1 (instead 2)

I fixed this issue for rounding date scripts for planning box, considering that:

start_date: 2008/01/01 00h00 stop_date: 2008/01/02 23h 59min 59 seconds

You can check: https://svn.erp5.org/erp5/trunk/products/ERP5/bootstrap/erp5_core/SkinTemplateItem/portal_skins/erp5_core/Planning_roundBoundToDay.xml

This is good for make planning box more consistent, but the dates (at task at least) should consider hours to make Planning Box more usable and consistent.