We have that the second law of Keppler applies here; they were the most important laws we had in order to start planetary motion for at least a century and they were:
1) the planets move in ellipses (with one focus on the sun)
2) A line joining the sun and the planet traverses equal areas in equal times
3) The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit.
Applying the second law, we get that the time to transverse A1A2 is double the time needed to transverse B1B2 (even though B1B2 is longer, because the planet is closer to the sun, it goes faster). The second law simply states that time is proportional to area in such graphs.