אבן העזר קכ״זEven HaEzer 127

Se’if 1א׳

צָרִיךְ לִכְתֹּב זְמַן, בַּגֵּט. וְאִם נִתְגָּרְשָׁה בְּגֵט שֶׁאֵין בּוֹ זְמַן, לֹא תִּנָּשֵּׂא; וְאִם נִשֵּׂאת, לֹא תֵּצֵא, אֲפִלּוּ אֵין לָהּ בָּנִים:

You need to write the time in your divorce certificate (this document is written when you when married not when you get divorced). If you have a divorce certificate without a time then you can't get married. If you get married then you don't undo it, even if you don't have children.

Se’if 2ב׳

אִם הָיָה מֻקְדָּם, אוֹ נִכְתַּב בַּיּוֹם וְנֶחְתַּם בַּלָּיְלָה שֶׁלְּאַחֲרָיו, פָּסוּל, אֲפִלּוּ הָיוּ עֲסוּקִים בְּאוֹתוֹ עִנְיָן. וְיֵשׁ אוֹמְרִים דְּנִכְתַּב בַּיּוֹם וְנֶחְתַּם בַּלַּיְלָה שֶׁלְּאַחֲרָיו, בִּשְׁעַת הַדְּחָק כָּשֵׁר. הַגָּה: וְגֵט מֻקְדָּם, אַף עַל פִּי שֶׁפָּסוּל, אִם קִדְּשָׁהּ אַחֵר, צְרִיכָה גֵּט מִשֵּׁנִי וַאֲסוּרָה לַחֲזֹר לָרִאשׁוֹן (פִּסְקֵי מהרא"י סִימָן י"ג לְדַעַת הָרַמְבַּ"ם, וּבֵית יוֹסֵף בְּשֵׁם הָרַ"ן וְהָרַשְׁבָּ"א):

If it was dated early, or if it was written during the day and signed the night after, it is invalid, even if they were discussing that matter. And there are those who say that if it is written during the day and signed the night after, in times of distress, it is valid. Hagah: And an early-dated get, even though it is invalid, if another man betroths her, she needs a get from the second, and she may not return to the first (Piskei Mahari, siman 13, according to the Rambam, and Bet Yosef in the name of the Ran and the Rashba).

Se’if 3ג׳

נִכְתַּב בַּיּוֹם, וְלֹא הִסְפִּיקוּ לְחָתְמוֹ עַד הַלַּיְלָה, אִם כָּתְבוּ בּוֹ קֹדֶם חֲתִימָה: גִּטָּא דְּנַן אִכְּתוּב בְּיוֹם פְּלָן וְלֹא הִסְפִּיקוּ סָהֲדֵי לְמִחְתְּמֵהּ עַד לֵילְיָא, וְחָתְמוּ הָעֵדִים אַחַר כָּךְ, כָּשֵׁר:

If it was written during the day and they didn't have time to sign it until night, if they wrote in it before the signing: This get was written on such-and-such a day and the witnesses did not have a chance to sign it until night, and the witnesses sign after, it is valid.