If a prayer was said a few minutes passed chatzot, does it still count in G-d’s eyes or simply not anymore?
(In terms of Shacharit).
The time for shacharis essentially is until the end of the 4th hour of the day, b’dieved one may still daven shacharis until midday, however after chatzos one should not daven shemona esrei of shacharis. (In retrospect if one already davened, he does not have to daven shacharis again). What should be done is the following. If the reason the person didn’t daven yet was accidental and not out of total negligence, then the person can daven a “tifilas tashlumin” a makeup tefila. the rule is that a makeup tefila may only be said, adjacent and after the tefila that is supposed to be said at that time. Therefore the person should wait until after zman mincha gedola, which is approx. half an hour after chatzos, daven mincha, by saying ashrei, and the shemona esrei for mincha. Then say ashrei again, as an introduction to the tefils tashmlumin, and then daven another shemona esrei- this one to make up the shacharis that was missed.
Rema O:CH 89-1, M:B ibid 7, O:CH 108-1, M:B 1, 2.