Is it permissible to supplicate for guidance for non-Muslims or atheists, and to what extent is it possible for this supplication to be answered, especially given the verse, "Indeed, you do not guide whom you love, but Allah guides whom He wills. And He is most knowing of the [rightly] guided"? And can a supplication be answered by achieving the specific request, or might it be delayed until the afterlife or avert an evil?

May Allah reward you for your eagerness to guide people. There is no blame upon you for supplicating for them by name, and there is no objection in that to Allah Almighty's decree. This is because their guidance is possible, and supplicating for their guidance is not a supplication for something impossible, which would make it forbidden. You should not stipulate to Allah Almighty that He answer you in a specific manner, for the matter belongs to Him, Glorified be He, and He does what His wisdom necessitates. So supplicate as you wish, and you will be rewarded for your supplication and your good intention. Then, leave the matter of how the answer manifests to what the wisdom of the Lord, Glorified and Exalted be He, dictates.