Reference for Taanit 2:7

אַנְשֵׁי מִשְׁמָר מֻתָּרִים לִשְׁתּוֹת יַיִן בַּלֵּילוֹת, אֲבָל לֹא בַיָּמִים. וְאַנְשֵׁי בֵית אָב, לֹא בַיּוֹם וְלֹא בַלָּיְלָה. אַנְשֵׁי מִשְׁמָר וְאַנְשֵׁי מַעֲמָד אֲסוּרִין מִלְּסַפֵּר וּמִלְּכַבֵּס, וּבַחֲמִישִׁי מֻתָּרִין מִפְּנֵי כְבוֹד הַשַּׁבָּת:

The priests on the weekly duty may drink wine at night, but not during the day; the officiating priests may not drink it either by day or night. The priests of the weekly watch, and the standing men are prohibited from shaving their beards, and washing their clothes; but, on Thursday, they are allowed to do so, in honour of the [approaching] Sabbath.

Jastrow