Forgot Al Hanisim and Hallel

If one forgot all hanisim and hallel and only remembers after they finish davening, can they still say either? What if it is still before chatzos, can they say hallel?

A – Say hallel, no need to repeat amidah for al hanissim.
Q – And what about after chatzos? Can one still say hallel?
A – Yes

RABBI SHAY TAHAN