You look at something and think "I don't want to think this through now but once I do I bet I can do it in three hours." So your next action is "Find three hours in my schedule to think through and deal with xxx." That's all you have to do.
Originally Posted by AlexanderChow
I prepare all my course lectures the night before if I can. Why? Because I know it will take me about that much time, and the material will be fresh in my mind the next day. On the other hand, I will have small next actions like "Jot down ideas for midterm" on a list because at some point I will look at that item, have an idea and jot it down. Effective doing is often the path of least resistance.