1) It should be immediately after reciting or hearing.
2) If you can do it in a way that does not disrupt the congregation then you should prostrate and restart your prayers. Otherwise normally it is not allowed to delay, obligatory prostration, however, in such circumstances, it might be OK.
3) There are four places that it is obligatory to prostrate, and the rest are recommended. https://duas.org/Misc/sajdadua.htm