In this instance, the printer’s manuscript originally read just like the 1830 edition, namely, without the Hebraistic and between the subordinate when-clause and the following main clause. It appears that scribe 2 of 𝓟 omitted the and, as did the 1830 compositor, since Oliver Cowdery supplied the and (as an ampersand) in 𝓟 when he proofed 𝓟 against 𝓞. The and is unexpected here, so it is very probable that the original manuscript had the ampersand. For the latter part of the Book of Mormon text, the 1830 compositor consciously removed many of these extra instances of and. See under Helaman 16:10 for some discussion of this editing on his part as well as a list of examples where he omitted the and in the latter part of the text. The critical text will restore the and here in 3 Nephi 23:8. For a list of other cases where the Hebraistic and was removed after when-clauses, see under 1 Nephi 4:8–9; also see the more general discussion under hebraisms in volume 3.
Summary: Restore in 3 Nephi 23:8 the Hebrew-like and that originally occurred after the when-clause and before the main clause; although both scribe 2 of 𝓟 and the 1830 compositor omitted the and here, Oliver Cowdery supplied it when he proofed 𝓟 against 𝓞 (undoubtedly because 𝓞 had it).