Longstreet said:
Here is a link to the 2-hour interview I mentioned. It is excellent and I viewed the entire interview. However, the part where the question about 1 hour next actions and the calendar starts at about 1:48:39. Enjoy!
https://www.youtube.com/watch?v=UKSyB1UOuNs&feature=youtu.be
I have just watched this segment. First of all thank you for posting the link. Great stuff. I plan to watch the full interview later (it's two hours, so I guess I should block it out on my calendar!

)
All kidding aside, here is my interpretation of what David Allen said:
I believe a good approach would be a
combination of what
Folke states — keeping the calendar sacred for date/time specific items such as meetings, appointments, etc. combined with a
review frequency status indicator — and making commitments with yourself on the calendar for long tasks (greater than one hour). You could basically keep these tasks on your next actions list with the appropriate status indicator, but
not on the calendar, until you decide it's time to move on that task/project. At that time (probably during a weekly review), you can then block out the time on the calendar because you have already decided it is now something that you will work on and that you want to move forward.
I don't see any value in putting a task that takes longer than one hour on the calendar to make sure it moves forward
just because it's a long task. I also must decide that this task is
now important enough, given my other priorities, that I want to commit to doing it now instead of later. Only then will I block out time on my calendar for it.
This is not something I have been doing but I see the value in giving it a try. I usually try to break down my long tasks into the shortest possible block of time needed to make progress on it (so I don't normally complete the task right away), but I think scheduling a longer block of time with myself could be very useful.