As a preliminary question for "yaakov's-hurry-to-have-kids-at-84":
On the Posuk (Gen 29,21) "וַיֹּאמֶר יַעֲקֹב אֶל־לָבָן הָבָה אֶת־אִשְׁתִּי כִּי מָלְאוּ יָמָי וְאָבוֹאָה אֵלֶיהָ׃" Bereyshis Rabba 70,18 explains that Yaakov was 84 and knew that he's destined to have the 12 tribes:
"אֶלָּא כָּךְ אָמַר לוֹ, אָמַר לִי הַקָּדוֹשׁ בָּרוּךְ הוּא שֶׁאֲנִי מַעֲמִיד שְׁנֵים עָשָׂר שְׁבָטִים, ..."
When did G-d tell Yaakov that he will have 12 sons?