Calculate hours when only one day is left.

This {% widthratio %} trick is something I found online that didn't
require a django-math module to work, but I would have rather written
something that:

(b) Could have a different message when there is only one hour
left: “less than one hour left” (i.e., tested if hours == 1)

(c) Will say “hour” instead of “hours” when there is exactly 1 hour
left.