If you are going to use a rule like this, you really need agile project management to guide what you are going to need. If you are doing Scrum properly, you pla

If you are going to use a rule like this, you really need agile project management to guide what you are going to need. If you are doing Scrum properly, you plan the features (and internal architecture needed for those features) for up to a month at a time, but you don't architect for purely internal things more than a month in advance (the YAGNI principle) since one of the Scrum principles is to limit work in progress. If you are doing a waterfall PM process, it doesn't apply so much.