The Midrash says: Whoever adds from the weekday to Shabbos, his soul will be paid back measure for measure in the World to Come.  If, Heaven forbid, his soul is in Gehinnom, it will be taken out of Gehinnom on erev Shabbos as early as the time he added to Shabbos in this world; and the same goes for motzei Shabbos.  The soul of a person who did not add to Shabbos will be let out of Gehinnom very late on erev Shabbos. ~ Minchas Shabbos 76:9 as quoted by R’ Dovid Meisels