I find these drawings useful as they make ideas more explicit. With sen sen no sen, I think that the relevant drawing is the first one (top left corner) but the timing of nage's entry is ahead of uke's expectation.
Great. But stuff about timing is kind of peripheral to the actual mechanics of it. Ie: discussions on sen-no-sen, go-no-sen etc can be misleading because they focus on the "when" rather then "how". The how is going to be the more important part, IMO.