The writers are holding off on the big Peter reveal for what I assume will be the season finale. They are, however, not putting it off and constantly reminding us of the implications and Walter's angst. This recurring thread with the typical MOTW stories works well together and has made the second half of the season very strong. Rather than push the alternate world/Observer/war/whatever convoluted thing is thrown in, the writers have made these past few episodes character based, focusing on Walter. John Noble knocks it out of the park each time, which is even more reason to continue the show like this.
I was afraid "White Tulip" would become one of those timeloop episodes where similar but funny occurrences happen over and over again, especially since Fringe is already a stock sci-fi show. The episode became much more, using Walter to parallel Alistair Peck (Peter Weller!), an astrophysicist that turns to time travel after his fiance dies. There is a poignant moment when Walter tells Peck his belief in God and that God has punished him everyday. Ultimately, the investigation was useless since Peck back in time nullifying everything, but he manages to send a letter to Walter with the simple sketch of the white tullip, Walter's sign from God.
The time travel in Fringe is interesting. There is a single thread running and everyone on it is constant. Traveling back and forth through time displaces the version in that time, so there is no chance that the same person can bump into him/herself from a different time. It's probably not relevant, but it's something to think about.
Score: 8.9/10
