Earliest time to make an Eiruv Tavshilin

Question

When's the earliest time one can make an Eiruv Tavshilin on erev yom tov?

Answer 1

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Lchatchila the Eruv should be made on Erev Yom Tov - anytime starting from the night before (Orach Chaim 527:14). According to the Biur Halacha the food used in the eruv should preferably have been baked or cooked on Erev Yom Tov.

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If it was made earlier - Lchatchila he should make another one without a Bracha on Erev Yom Tov (Orach Chaim 527:13). Bdieved it can be made earlier so long it is done with a food item that will last and it should be done without a Bracha and a Tenai (Minchas Aharon 1 Siman 145)

Answer 2

With regards to the earliest you can make the Eruv on Erev Yom Tov (your actual question), The Nitei Gavriel (Laws of Yom Tov II 81:10) says you can even make it the whole day, even in the morning (meaning not the night before). In the footnotes he explains none of the earlier authorities address this issue, but it appears that it is better to wait till morning. See there for more sources and information.

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If you did do it earlier than Erev Yom Tov, he quotes The Shulchan Aruch Harav (527:2) as having said you've fulfilled your obligation (Bedi'eved), but should do it again without a blessing.

A little more depth:

The Talmud (Beitzah 15B) gives us two reasons why we make an Eruv Tavshillin, brought here:

a) Concern for the honor of yom tov: This injunction impresses on people the importance of yom tov. After all, it is forbidden to prepare on yom tov even for the sake of the holy Shabbat. How much more so is it forbidden to prepare on yom tov for a following weekday!

b) Concern for the honor of Shabbat: When Shabbat follows yom tov, there is the concern that one's attention will be focused on yom tov, which arrives first, and pay less attention to the Shabbat that follows. The eruv tavshilin compels the person to begin preparation for Shabbat even before yom tov begins, thus reminding him to reserve choice dishes for Shabbat, too.

In the Shulchan Aruch Harav (527:2), he brings practical halachic differences between the two reasons. If you want to impress on people the importance of Yom Tov, you could make the Eruv Tavshillin weeks in advance (assuming the cooked food will survive), and one Eruv could be made for many Yomim Tovim.

If however, you want to impress on people the importance of Shabbat, you must make the Eruv only on right before the holiday, and only for that holiday. Otherwise, you won't be remembering the importance of Shabbat.

Therefore, you should really only make the Eruv before Yom Tov, and only for that Yom Tov.

If you did make an Eruv a while before (intending it to cover this Yom Tov), and you forgot to make another Eruv before the Chag, you've can rely on the first Eruv you made. However, if you remember before Yom Tov you should make a new Eruv or take the old Eruv and say "With this I will be able to cook...", but don't make the blessing.