Reference for Negaim 3:5
הַנְּתָקִין מִטַּמְּאִין בִּשְׁנֵי שָׁבוּעוֹת, בִּשְׁנֵי סִימָנִין, בְּשֵׂעָר צָהֹב דַּק וּבְפִסְיוֹן. בְּשֵׂעָר צָהֹב דַּק, בַּתְּחִלָּה, בְּסוֹף שָׁבוּעַ רִאשׁוֹן, בְּסוֹף שָׁבוּעַ שֵׁנִי, לְאַחַר הַפְּטוּר. וּבְפִסְיוֹן, בְּסוֹף שָׁבוּעַ רִאשׁוֹן, בְּסוֹף שָׁבוּעַ שֵׁנִי, לְאַחַר הַפְּטוּר. וּמִטַּמְּאִין בִּשְׁנֵי שָׁבוּעוֹת, שֶׁהֵן שְׁלשָׁה עָשָׂר יוֹם:
Hairless patches are made impure after two weeks or through two signs: thin yellow hair or expansion. Regarding thin yellow hair, [it is made impure] initially, at the end of the first week [of quarantine], at the end of the second week [or] after the exemption. And regarding expansion, at the end of the first week, at the end of the second week [or] after the exemption. And they are made impure after two weeks, which are [actually] thirteen days.