The three options
Set this in Settings, then Yahrzeit. Shabbat before. The name is read on the Shabbat preceding the anniversary. This is the default, and the most common practice: it gathers the week’s yahrzeits into the service the community is already at, and it reaches the family before the day itself rather than after. Day of. The anniversary itself, whichever day of the week that is. Shabbat after. The Shabbat following the anniversary.This is a congregational setting
It applies to every yahrzeit record. You cannot set one family’s observance to the Shabbat before and another’s to the day of. That is intentional. Observance timing is a matter of how your community runs its services, not a per-family preference, and a mixed setting would make your weekly list impossible to read.What it does and does not affect
It affects how observances are presented for your congregation’s practice, so the office can work out what is read on a given Shabbat. It does not affect the anniversary date itself. A yahrzeit on 12 Cheshvan is on 12 Cheshvan regardless of this setting. It does not change how far ahead reminder emails go out. That is a separate setting. See Reminder emails.The two settings work together but are independent. If you announce on the Shabbat before and send reminders seven days ahead, most families get their email roughly a week before the anniversary and hear the name read the Shabbat before it. Whether that ordering suits your community is worth a moment’s thought when you set the reminder lead time.