I would put a due date on the project. From my weekly review, I would know the project due date was coming up, and I would spend 1-2 hours a day in the early morning working on it until it was done. I could actually schedule time in my calendar for "meetings with myself", but I don't find that I need to do this. I might also spend other available time during the day on the project, depending on context, time available, and energy. Because I use software that supports flagging, I might use this feature to flag some of the next actions.
I know this sounds like a textbook answer, where the GTD book is the textbook, but it really does work. This past week I had three such projects: high importance, firm deadline, each of around 6+ hours duration, all done by Friday. I worked steadily on all three during the week. I gave a talk to a local group Friday night, got home at midnight, then spent 12:30-4:30 AM at the ER due to a family emergency. I did miss my usual Saturday weekly review, so I need to do it today (Sunday). I don't think I'm a particularly organized person, and I'm also pretty sure I haven't reached the limits of what is possible.