once you get to 4 TPOs then you are looking for the possibility that the trade alters from responsive to initiative. if it does not occur by this time then the chances of a trend day are lessened and so from 8 TPOs you are then effectively looking at a new IB distribution that frequently becomes a late running profile. ES on Fridaty Jun 8th was just such a clssic one in that respect.
Back in 1986 Pete
Steidlmayer wrote about needing to wait for the first 4.5 hours in ES to pass before establishing a trade and as per usual I contend nothing has changed over the years