On current development builds, when a task's due date is:

• on the same day of the week as today, but a week or more apart
• is due later in the day than the current time (today)

then the "Due In" column incorrectly displays "0 days".

The code that generates the "Due In" column string is the "duration" method in "comm/calendar/base/content/calendar-task-tree.js", around line 360.

It turns out the duration object can be like { weeks: 1, days: 0 }, so we have to convert weeks to days. For example:

6 day duration is like: { weeks: 0, days: 6 }
7 day duration is like: { weeks: 1, days: 0 }
8 day duration is like: { weeks: 0, days: 8 }

(The zeros are actually negative: -0.)

Revised the comment to make it really clear what's going on.

Pushed by mozilla@jorgk.com:
https://hg.mozilla.org/comm-central/rev/2a299189d890
Fix the "0 days" error in the task "Due In" column. r=philipp

TB 68 beta 4 / Cal 7.0 (well, just aligned that version with TB):
https://hg.mozilla.org/releases/comm-beta/rev/3355ea2d0afb1816d437f23dd53380dcc6d95926