In ta’anis (1:5-7) the Mishnayos discuss how and when to fast for rain in a drought, for example:
הִגִּיעַ רֹאשׁ חֹדֶשׁ כִּסְלֵו וְלֹא יָרְדוּ גְשָׁמִים, בֵּית דִּין גּוֹזְרִין שָׁלשׁ תַּעֲנִיוֹת עַל הַצִּבּוּר.: עָבְרוּ אֵלּוּ וְלֹא נַעֲנוּ, בֵּית דִּין גּוֹזְרִין שָׁלשׁ תַּעֲנִיּוֹת אֲחֵרוֹת עַל הַצִּבּוּר.
If kislev comes, and rain hasn’t fallen, beis din declares 3 fasts (Monday, Thursday, Monday) on the nation... If those pass and weren’t answered (with rain) beis din declares another 3 fasts on the nation...
How did beis din know when enough time had passed for it to be considered unanswered? Was there a set amount of time that they waited, or did each beis din decide for itself when enough time had passed?