Can you give me a definite answer by tomorrow?

你最晚明天能给我一个确定的答复吗？

《牛津词典》

You'd better talk it over with your wife and give me your answer tomorrow.

你最好和你的妻子商量一下，明天给我一个答复吧。

youdao

A: it sounds all right to me, but I will have to think about it. I'll give you a definite answer tomorrow.

我是觉得不错，但我得想一想，明天给你答复。

youdao

Trying to make appointments with people is sometimes impossible - "Call me tomorrow, who knows if we'll still be alive then" is often the answer.

BBC: NEWS | Middle East | Constitutional impasse in Lebanon