Q. A person who is davening Maariv on motzoi Shabbos 50 minutes past sunset, and his custom is to prolong Shabbos for 72 minutes, or longer, should he skip ata chonantanu in SE, because once he says this prayer, his Shabbos is automatically over and he fails to comply with the mitzva of tosefes Shabbos? Should he recite the first three brachos extra slowly in order that his recitation of the Havdalah will take place after 72 minutes?
A. Horav Shlomo Miller Shlit’a explained that adding time to Shabbos and maintaining Rabbenu Tam’s zeman is basically a reference to the prohibition of doing work until that time has arrived. The fact that he recited ata chonantanu, does not permit one that keeps usually Rabbenu Tam to do melochos until the right time has come. By adding a short time, he can also comply then with tosefes Shabbos.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a