There is a custom to perform "Hatarat Nedarim" (dissolving of vows) on Ereb Shabbat. One of the sources for this practice is from the Hida (Rabbi Hayim Yosef David Azulai, 1724-1807) in his Shiyureh Beracha (YD 211:1) who testifies that the great Mekubal, the RaShaSh (Rav Shalom Sharabi, 1720-1777, Jerusalem), instituted the custom to perform the dissolving of curses every Ereb Shabbat before Minha. This was also the custom of the Yeshiva of Mekubalim of Bet El.
The idea behind the practice is to enter Shabbat spiritually cleansed from the transgressions of vows, just as we enter Shabbat cleansed physically. The rationale of doing it prior to Minha is that this was the time on the sixth day when Adam sinned and the original curses befell him. Thus, it is the logical time to remove the curses. Nevertheless, Hacham Sha’ayo writes in his Mehkereh Ares (Vol. 8:78) that today, the custom is to perform this after Shaharit, since that is the convenient time when people are not as rushed as right before Shabbat.
SUMARY
It is a worthy practice to perform Hatarat Nedarim and Kellalot on Ereb Shabbat
