"i shouldn't say that yet" is right some more uses would be its not yet time or the time has yet to come If you have any more questions please be sure to run them through me ill be sure to help

Hi Gru, "Yet" roughly means "so far", or up till a certain time, and suggests the action is expected. We do use it with present perfect, but it's also typically used with "not", so your phrase is correct. It's possible to use it in a positive sentence, if we are expecting something to happen.