I’m still not following. I see how other nodes would start trying to reorganize or stop mining, but I don’t see how you infer a PTL from the FTL. Let me try to phrase this more formally. I think you are suggesting that we do not allow the timestamp to progress more than two hours between blocks, i.e. we require for each block B with height n
∀n∈N: nTime_{B_n} + 3600 s \geq nTime_{B_{n+1}}.
I’m afraid that I don’t see how this would allow us to infer
∀n∈N:time_{B_n}\leq time_{B_{n+1}} - 3600 s.
We can move the seconds over, but the inequality doesn’t change direction.