Kitzur Shulchan Aruch קיצור שולחן ערוך

When a bris or a pidyon haben occur on erev Tishah beAv, the festive meal should be held before noon.

You should not go for a walk on erev Tishah beAv; and in the afternoon, it is the custom to study only the subjects you are permitted to study on Tishah beAv.

Concerning the final meal before the fast, there are many laws. The correct custom is to eat a regular meal before the Minchah service. After that, you pray Minchah, omitting Tachanun, because Tishah beAv is called a Moed as it is written, "He has proclaimed a Moed for me" (Lamentations 1:15). Towards evening, you should sit on the floor but it is not necessary to take off your shoes. Three people should not sit down (to eat) together, so that they will not be required (to recite Birkas Hamazon) with zimun. You should eat only bread and a cold hard-boiled egg. You should dip a small piece of bread in ashes and eat it. You should be careful to finish the meal while it is still day. (Whether you are permitted to eat after this, see 131:12 below).

If a person fasts throughout the year on Mondays and Thursdays, and erev Tishah beAv occurs on either of these days, he should have his vow annulled. If someone observes Yahrtzeit on erev Tishah beAv, he should resolve on the first Yahrtzeit, to fast only until noon has passed, then he should pray Minchah gedolah (early Minchah), that is, half-an-hour past noon, eat a meal, and afterwards towards evening, he should eat the final meal.

During twilight, you are forbidden to do all that is forbidden on Tishah beAv. You must, therefore, take off your shoes before twilight.