Tosefes Shabbos (Adding to Shabbos): Mentally or Verbally?

Tosefes Shabbos (Adding to Shabbos) 

There is a mitzvah of Tosefes Shabbos, both on Erev Shabbos (the eve of Shabbos) and Motzoei Shabbos (when Shabbos is over). There is a discussion among poskim regarding how much time one should add. According to many poskim, the minimum is four minutes before shkiah (sunset) on Friday, and four minutes after tzeis hakochavim (nightfall) on Motzoei Shabbos. Of course, the more one adds, the greater the mitzvah; however, the time added on Erev Shabbos must be after plag haminchah, which is 1¼ “halachic” hours before sunset. Some poskim say that Tosefes Shabbos is achieved just by abstaining from doing melachah (work) which is prohibited on Shabbos. Other poskim state that it is also important to accept Shabbos b’dibbur (verbally) by davening Kabalas Shabbos (the Friday evening prayer recited prior to Maariv) or mentioning the kedushah (holiness) of Shabbos. However, this applies only to the time an individual wishes to add to Shabbos; the obligatory Tosefes Shabbos [at the time of shkiya] need not be verbalized.  #345?1

https://halacha2go.com?number=345

Practical Halacha: One minute a day. By Horav Yosef Yeshaya Braun, shlita, Mara D'asra and member of the Badatz of Crown Heights.