If a package was received on Shabbos unexpectedly, does one have to wait for some time after Shabbos before opening it?
If you or the sender did not intend to have it specifically arrive on Shabbos, then you do not need to wait at all.
If the package was intended to arrive on Shabbos, one would need to wait after Shabbos בכדי שיעשו -the amount of time it would take to do Melacha on Shabbos to send it.
שו״ע או״ח סי׳ תקטו סעיף ח . מ״ב ס״ק סו
שש״כ פרק לא סעיף כד