As discussed under verse 14, the original text allows the repetition of the subordinate conjunction that in complex sentences. Here in the original text for verse 26, we have a repeated that for the when-clause immediately following the initial “it came to pass” clause (“now it came to pass that when it was night that I caused …”). The 1920 LDS text removed the repeated that, but the critical text will restore it.
The editing out of repeated that ’s is quite uneven in the history of the text. Elsewhere in the original text, we have the following cases of the repeated that for a when- clause immediately following “it came to pass that”, and in only two cases has the repeated that been removed, both in the editing for the 1837 edition (each of these is marked below with an asterisk):
One reason the 1920 editors may have noticed the repeated that in Alma 58:26 is that there the when-clause is quite short (“when it was night”). When the when-clause is longer, as in the examples that escaped the 1837 editing, it is harder to notice the repeated that. In any event, the repeated that is very common in spoken English as well as in unedited writing (and even edited writing, as these examples show). For further discussion regarding the repeated that, see under that in volume 3.
Also here in Alma 58:26, Oliver Cowdery initially omitted in 𝓟 the subordinate conjunction that which comes after the past-tense verb form caused. Virtually immediately he supralinearly inserted the that (there is no change in the level of ink flow). 𝓞 is not extant here, but there is clearly room for it in the lacuna. Elsewhere in the text, a finite clause complementing the verb cause always takes the subordinate that (see the discussion under 1 Nephi 17:46). Here in Alma 58:26, there is a conjoined finite clause that follows the first one, and it too is headed by that: “but that they should march forward by another way towards the land of Manti”.
Summary: Restore in Alma 58:26 the original repeated that which follows the when-clause; this kind of redundancy is common in the original (and current) text; also maintain the that which follows caused.