Show time remaining for the AI planner to schedule.

For a 4-hour task:

If 1 hour is scheduled in the future, there are 3 hours remaining.

If 1 hour is scheduled and completed in the future, there are 3 hours remaining.

If 1 hour scheduled in the past, there are 4 hours remaining.

If 1 hour scheduled and completed in the past, there are 3 hours remaining.

If 4+ hours are scheduled in the future or complete in the past 0 hours remaining.

I want to see that remaining time so I can add time on if need be.