I just spent a few minutes figuring out when I need to start working on each goal (in the worst case where I haven't added any more to it than was needed to not derail yesterday). I needed to find some dead time for a new goal.

I suggest you add a table somewhere that shows all of a user's goals, their deadlines, the last possible time to start on them, and any "free time". This would only work for time based goals, of course. It'd make it easier to set up waterfalls, which are a good idea that is pretty non-obvious.