Class AB amplifier conduction angle
Judging from the single diagram you post, run away from those web pages.

It seems they've managed to make a simple concept difficult to understand, and got it wrong in the process.  What it appears that diagram is trying to show is how one of the transistors operates.  However, what they are showing is class B operation, not class AB.

In class B, each transistor only conducts for exactly half the cycle, as shown.  In class AB, there is a little crossover between the two transistors.  Exactly in the middle, they are both conducting some.  In the diagram you show, point Q should really be moved to the left a little, and the "output signal" biased up a little.

Added

Yes, your new diagram now shows true class AB behavior.