Ability to set time limits on each project instead of only due dates.
For example, I've got project X and for project X I only want to spend 8 hours per month working on the various things I need to do. So I set the project time limit to 8 hours, then I get to work.
As I'm working and logging my time, I get notified as I'm nearing the 8 hours. Something like 30 min before and as soon as I get to 8 hours.
Of course, I can continue working but now I know I've hit my project time limit. Then either the 1st of every month or on a day of my choosing, the time resets and know I've got another 8 hours to work in that specific project.