MB3 104a: Waiting Kedei Sheya'asu after Shabbos (307:19-22)

If a person violated amira l'nachri he can benefit from it but only after Shabbos ends plus the amount of time it takes to do the melacha. If it was done publicly, it's prohibited to him forever. Amira lenachri is prohibited even if you won't benefit from it. A shvut (including amira l'nachri) can be done during bein hashmashot for a mitzvah purpose. Hinting to a non-Jew to do a melacha.