If Tisha B’Av is coming on Sunday, when or what time is the last meal for Shabbat?
The last meal for Shabbat must end before sunset, since the fast of Tishah B'av begins at sunset.
As aish.com writes here
Although any food may be served, including meat and wine, and zemirot may be sung, the mood should be somewhat subdued.
A person should not say that he is eating in order to have strength to fast, but he may think this.
One must stop eating and drinking before sunset, since the fast begins at this time. People should be reminded about this, as it is unlike a regular Shabbat.