What are the earliest and latest times for reciting Kabbalas Shabbos? If one was too busy preparing for Shabbos to say it at the normal time, may one recite it at any time after Shabbos starts?
Earliest time for Kabbalat Shabbat
The earliest time for accepting Shabbat is Plag haMincha - 1¼ Halachic hours (Sha'ah Zemanit) before sunset. (Chabad have an online Halachic time calculator, with Plag and Sha'ah Zemanit for most locations, here.)
Source: Shulchan Aruch, Orach Chaim 267:2
וּבִפְלַג הַמִּנְחָה יָכוֹל לְהַדְלִיק וּלְקַבֵּל שַׁבָּת בִּתְפִלַּת עַרְבִית
So, it has been suggested, that one could start the Kabbalat Shabbat Psalms a few minutes before Plag and get to the "Shabbat Acceptance" moment right at Plag. This "Shabbat Acceptance" moment is generally defined as the last stanza of Lecha Dodi.
Latest time for Kabbalat Shabbat:
Background: Kabbalat Shabbat has 2 meanings:
- The original meaning: To accept upon oneself the sanctity of Shabbat. Even though Shabbat begins (and obligates you in all its Halachot) automatically at sundown, accepting Shabbat actively is done for two reasons. (1) To accept Shabbat early and fulfill the Mitzvah of Tosefet Shabbat (adding on to Shabbat), and (2) to actively accept the Mitzvah of Shabbat, instead of it happening by itself, and get the reward for keeping Shabbat on purpose.
Obviously, this Kabbalat Shabbat can be done at any point after Shabbat begins, to transform one's Shabbat observance from passive to active.
- The newer meaning: The Ari z"l in the 16 century (based on the Gemara in Shabbat 119a) instituted the Kabbalat Shabbat Service starting with certain Psalms and reaching a crescendo with Lecha Dodi followed by the Shabbat Psalms (92 and finally 93). Until then the entire Kabbalat Shabbat Service consisted of Psalms 92 and 93.
The point was to welcome the Shabbat Queen with a royal ceremony. The ideal time to do this is when the queen is on her way in.
Once that time has passed then the point of the ceremony is lost, but you still can say it, to transform your Shabbat observance from passive to active, since it's simply some Psalms and a poem.
Though welcoming the Shabbat Queen - with the Lecha Dodi poem - long after she's arrived seems rather peculiar.
To answer your question: I cannot find any Poskim who mention this, but I would propose that any time before the Friday night meal would still be somewhat appropriate to say Kaballat Shabbat.
Once you've wined and dined in honor of the Shabbat Queen, it seems silly to then start the Welcoming Ceremony. That said, the OU site write (without sources or explanations):
The latest time to finish saying Kabbalat Shabbat is before daybreak on Saturday morning.