In case you want a more passive solution, I do know that there are apps for Linux (and therefore most probably also they exist for Windows) that log window title and amount of time. When you feel like it, you take a look in the report, and summarize everything that you consider part of the project.
It's not perfect, but at least you won't have the task of starting/stopping the clock all the time. And this kind of solution also doesn't miss those small five-minute things that we tend to ignore to log manually.