Is it possible to schedule a task on a day without a time, but have a
duration?

I have several tasks that are not bound to a time, but will be done when I
have some spare time. It would be handy if there was a way the estimated
duration of those tasks so I can choose the right one.

And in general I find it useful to see how much work there still is to be
done.

-- 
Cecil Westerhof