[alleyb]

The answer to your question - for what in essence you are asking is when does the profile change from a responsive to an initiative style - depends on the type of trader you are. Let me make a comment that for the longer term horizon trader what Pete Steidlemayer referred to as the other time frame trader 5 points in the S&P is just a bid/offer spread.
Let us assume you are a day trader and a scalper at that and my comments are purely for the S&P for it differs depending on product.

To look purely at the TPO and try to set a rule of when does it become a fat profile is not sufficient.... for volume as well as time together with the value all in relation to previous as well as current pattern make up the market profile..... BUT...... the short answer to your question is 8 TPOs and to be on look out once 4 have formed

Looking at the slightly longer term profile of composite days then the moment that you get 22 is time to be aware of the possibility of change. And once you reach 42 you should be monitoring in ultra-short term mode because at 48 that is about the point of time that change occurs.