Have eaten vs. ate

There are a number of threads for the present perfect on this site so I will not repeat all of them.

One of the uses of the present perfect is to talk about an action in the past in a time frame that has not yet finished.

I have eaten breakfast this morning. (present perfect) You can use this if it is still "this morning"
I ate breakfast this morning. (Simple past) when the

Sorry I can see I didn't answer all your questions.

For the two sentences with "today" both are correct. The one used will depend on how the speaker feels about "today" and whether he feels the day to be over.

I didn't eat breakfast today. (and now it is too late)
I haven't eaten breakfast today. (maybe there is still a chance?)

Thank you, Louise, for your helpful response.

I now understand the meaning of the examples with the expression 'this morning'.
In the case of the expression 'today',

I didn't eat breakfast today. -- Does it mean it's already night time when I said this, although it's still within the 24-hour time frame?

I have not yet eaten breakfast

AnonymousI didn't eat breakfast today. -- Does it mean it's already night time when I said this, although it's still within the 24-hour time frame?

It might not be night time but you consider the day to be finished, or at least too late to eat breakfast.

AnonymousI have not yet eaten breakfast today. -- Is this correct because the 24-h

I'm sorry, I wasn't able to read your response right away due to posting delay. All my questions have now been answered. Thank you very much for your assistance. I now understand.