Havdalah when Tisha B’Av falls on a Sunday

Hello Rabbi,
 
Someone who wants to break the fast on Shabbat from the day after the offering of the offering, and not wait until the end of the fast (for fear that he will forget and for other reasons): Can he eat after the havdalah? The column writes in the 1955 sign in the name of the hab, who is not even allowed to break the fast, because in the havdalah he accepts the fast and is forbidden to drink wine. But that sounds a bit strange – is there such a thing as accepting the fast early? Or maybe Tisha B’Av, which I think is an addition?
 
In practical terms, do you think it is permissible for me to separate on Shabbat and drink wine as usual? If so, is it permissible to continue eating and drinking until sunset?
 
thanks