220:4 If a person buried a close relative seven days before yom tov, since he sat shiva before yom tov, the holiday cancels the restrictions of shloshim. This is the case even if the last day of shiva was on erev yom tov since we say that part of a day is like a whole day. After leaving shul, the shiva is completed and the rest of the day is considered part of shloshim, which the holiday cancels. The mourner is permitted to wash his clothes, bathe, and shave on erev yom tov close to dark since he would be doing so in honor of the holiday, which cancels the restrictions of shloshim.
On erev Pesach, since the time for slaughtering the korban Pesach (Passover offering) was after midday, this time is considered a little like a festival. The mourner is therefore permitted to wash immediately after midday. He may shave before midday because after midday another person would not be permitted to shave him (or cut his hair).
220:5 If the last day of shiva will be on erev Shabbos, and Shabbos is erev yom tov, the mourner is permitted to wash his clothes, bathe and shave on Friday.