Say you have a project with a sequence of actions 1 then 2 then 3.
You do your weekly review, well, weekly.
1. is your *next* action, so you put it in a next action list.
You complete 1. but have no trigger to do 2. until after your weekly review. So the project is stalled for the remainder of the week (unless your unconscious triggers you -- but that misses the point of GTD).
So you only get triggered to do one next action per week on this project -- and the project would implicitly take you at least three weeks to complete...
Maybe I'm missing the GTD zen on this one -- how do you folks avoid this problem?