Martin Ehrensvärd says that post-Exilic Old Testament books show evidence of early Hebrew.
Martin Ehrensvärd, “Linguistic Dating of Biblical Texts,” in Biblical Hebrew: Studies in Chronology and Typology, ed. Ian Young (London; New York: T&T Clark, 2003), 175-176, 181
As I stated in my introduction, the second weakness of Hurvitz’s argument is that it is clear that EBH was in use in post-exilic times: most scholars date the books of Isaiah 40–66, Joel, Haggai, Zechariah,48 and Malachi to (very late exilic/) post-exilic times, even though complete consensus pertains to Haggai and Zechariah 1–8 only. Authorities make the following statements regarding the language of these books (all translations are mine); on Isaiah 40–66:
. . . like the language of Haggai and Zechariah—and to an even greater extent—the language of ‘second Isaiah’ is well anchored in classical Hebrew and the imprints of late biblical Hebrew are quite scanty. (Hurvitz 1983a: 215 = 1997: 21)
. . . almost perfect classical Hebrew. (Rabin 1988: 16)
. . .
In his 1996 study, Rooker, more or less explicitly arguing for an eighth-century date of the text, analyzes some features of the Hebrew of Isaiah 40–66 and compares them to LBH features of Ezekiel. He points to nine orthographical, morphological, lexical, and stylistic features (analyzing four of them) where Isaiah 40–66 consistently shows EBH usage and where LBH usage is found in Ezekiel. He states in his conclusion that ‘… Ezekiel, from the exilic period as well as post-exilic Hebrew literature always indicates later linguistic features than those we find in Isaiah 40–66’ (Rooker 1996: 312).