I am Nobody.
What do I know?
Well I will tell you.

We will know by the END OF SEPTEMBER. If it were a spacecraft, the best time for it to maneuver would be at the closest approach to whatever it is orbiting. This is because of the Oberth effect.. effectively the faster youre going the mpre efficient your burn, and the closer the orbit, the faster it is. Even on a parabolic orbit, this means that you get a speed boost proportionate to how close you get to a world. At its closest distance (periapsis) to Mars in its current course, it would gain only a marginal, almost negligable bonus to its burn. Any time between now and then, a spaceship could burn to adjust that periapsis closer to Mars so that the eventual burn near mars would be far more efficient. If it doesnt adjust its course it was a comet.
If it does.. dont get on the ships.

Need I remind you that the rapture does not actually appear in scripture?