Oliver Cowdery initially wrote “the time is at hand” in 𝓟, then supralinearly inserted now (without any change in the level of ink flow). It is doubtful that he was editing the text here since elsewhere in the Book of Mormon we have no other occurrences of “the time is now at hand”, but there are seven occurrences of “the time is at hand”. In other words, Oliver initially wrote the expected phraseology in 𝓟, then corrected 𝓟 to agree with the reading of 𝓞 (no longer extant here, but which undoubtedly had the now). The use of the adverb now in this phrase is supported by the occurrence of another adverb of time, soon, in Alma 10:23: “the time is soon at hand”.
Summary: Accept in Alma 60:29 Oliver Cowdery’s corrected reading in 𝓟, the adverb now in “the time is now at hand”.