Sujood Saho is part of a Hadith by Bukhari. Here is a translation of one hadith:
Aalqama said: Abdullah Ibn Masoud said, “The prophet (SAAW) prayed (and) Ibrahim (Al Nakh’ie) said, ‘I don’t know if (the prophet) added or missed!’ After (the prophet) finished the prayer with tasleem, the companions asked him, ‘O prophet of Allah, was anything new given in Salah?’ The prophet asked why they asked. The companions said, ‘You did something different than was known to us!’ The prophet rolled his feet and faced Qiblah and prayed 2 sujood (prostrations), then made tasleem (salam) again, and when he turned toward us he said, ‘If something new was revealed during Salah I would have told you about it, but I am human like you (and) I do forget like you forget, so if I forget, remind me, and if someone is doubtful about his Salah let him seek what is right and continue his prayer, then make tasleem and pray two sujood.’” Hadith narrated by Bukhari.
As you can see even after finishing Salah you can do the sujood. I am not sure if there is a time limit on this, but it seems unlikely as none is mentioned. There is a number of rules at the bottom of the page that may clarify on some scholarly deductions. There is a number of other Hadiths giving examples: Abu Hurairah/Ibn Buhaina