וַיִּשְׁלָחֵ֣ם לְבָנ֗וֹנָה עֲשֶׂ֨רֶת אֲלָפִ֤ים בַּחֹ֙דֶשׁ֙ חֲלִיפ֔וֹת חֹ֚דֶשׁ יִהְי֣וּ בַלְּבָנ֔וֹן שְׁנַ֥יִם חֳדָשִׁ֖ים בְּבֵית֑וֹ וַאֲדֹנִירָ֖ם עַל־הַמַּֽס׃ (ס)
Rashi on I Kings
In shifts. As he concludes and says, “they will be a month in Levanon.” When the ten thousand men were in Levanon in Tishrei and the twenty thousand men were at home in Mar Cheshvan, the second ten thousand would alternate and go out to Levanon and these would return to their home[s]. And in Kislev the third ten thousand would go out to Levanon, and these [second ones] would return to their home[s]. And in Teiveis the first ones go out and return to Levanon, and thus they would continue the cycle, which resulted that each ten thousand among them spent one month in Levanon and two months at home.