The Idea in Brief
The BHS emendation is not justified. In this regard, the Masoretic Text contains helpful hints in understanding ambiguous words. That is, the Masoretic Text correlates the verb in Gen 8:10 and Gen 8:12, but with a different verb. Based on these Masoretic tips (discussed in the next section), the best reading of this verse would appear as follows:
10 So he entered yet upon another seven days; and again he sent out the dove from the ark.
The Masoretic scholars did not take the modern view that this verb was חוּל (khül), which means to wait anxiously (Pual stem), but the verb חָלַל (khä·lal'), to enter upon (Hifil stem) with the waw consecutive, which comes from the root to penetrate and to defile, which leads to the idea of breaking or opening something, which is evident in the Masoretic Text.
Masoretic Margin and Footnotes
There are helpful hints to understanding the meaning of ambiguous words in the Hebrew Bible. For example, In the Book of [First] Chronicles, the exact same word with the exact same consonants and vowel points appears in the following verse with comments in the margin and footnotes of the Masoretic Text -
1 Chr 10:3 (NASB)
3 The battle became heavy against Saul, and the archers overtook him;
and he was wounded (וַיָּחֶל) by the archers.
This verb is Hifil stem from the same verb חָלַל (khä·lal'), and so by the bow, (the arrow) "penetrated" because of the archers. On this particular page in the margin and at the bottom of the page in the Masoretic Text (Page 671 of the Codex Leningradis) appears as follows. Please click the image to enlarge.
This particular verb with this particular vowel pointing occurs nine times in the Masoretic Text (signified by the term "ט̇"), and the first citation of the first instance of the appearing of this verb is Gen 8:10, which is indicated by the blue box (first two words of Gen 8:10) in the image above.
The image below is an amplified view of the same footnotes (from the image above). Since the Masoretes did not use a system of chapters and verse numbers (which Christians later developed) they had to use their memory! That is, they referenced Scripture "verses" by citing the very first few words of that verse, which implies that the Masoretes had vast portions of the Hebrew Scriptures MEMORIZED. For example, see the image below (and please click to enlarge).
The image below is the transcription of the same nine verses made by Gerard Weil, who was contracted by the editors of BHS to document all the Masoretic margin notes, footnotes, and end notes of the Codex Leningradis.
In summary, the Masoretic editors (who had command memorization of the Hebrew Scripture) viewed this grouping as the SAME VERB FORM of חָלַל (khä·lal'), Hifil stem. That is, they never "mixed and matched" identically written words (or homonymous words) that had different meanings, but only words with the same spelling and/or the same vowel pointing if and when such words were of the same "lemma". In this case, they lumped together the instances where the Hifil form of the verb חָלַל (khä·lal') appeared in the Masoretic Text with the same (or very similar) vowel pointing. In this respect, these Masoretic helpful hints are priceless when trying to understand the Hebrew Scriptures. In summary, the Masoretic reading follows other Jewish sources as well.
Finally, the Aramaic translations of the Hebrew Bible attest to the same. These translations appeared more than five centuries before the Masoretic Scholars appeared. For example, the Targum Onkelos appears as follows, which includes a variant reading to help convey the idea!
Please notice that the first words of Onkelos are "וְאֹורֵיך (ושׁרי) עֹוד" which means, "he prolonged (or allowed) another [seven days] ..." In other words, the Targum here leans more toward the idea of extending time by seven days. As noted above, the Masoretic Text takes the same approach, because the Masoretes saw the verb חָלַל (khä·lal') here.
The Targum Neofiti appears as follows:
Please notice that the first words of Neofiti are "ושרי תוב" which means, "he permitted again [seven days] ..." In other words, the Targum here leans more toward the idea of extending time by seven days. As already mentioned, the Masoretic Text takes the same approach, because the Masoretes saw the verb חָלַל (khä·lal') here.
In conclusion, according to the Masoretic Text, the verb in Gen 8:10 is the same verb חָלַל (khä·lal') found in Gen 9:20; Nu 25:1; Judg 16:22; 1 Sam 31:3; 1 Chr 10:3; Jon 3:4; 2 Chr 3:1; and 2 Chr 3:2 (and 2 Ki 1:2 and Gen 8:12). In other words, depending on the aspect, tense, and mood this verb means to penetrate > to defile and therefore includes the meanings of to enter upon > to begin > etc. Thus in Gen 8:10 and in Gen 8:12, the meaning would be to enter upon.
That is, "Noah entered yet upon another seven days..."