the present perfect tense with an incomplete period of time

Question

I turned off the light before leaving this morning.

If 'this morning' is not over yet, is 'have turned off' also OK?

Because the present perfect tense is used to express actions happening in an incomplete period of time (source).

Answer 1

You are talking about the period of time before you leave. So,this period of time finished.

You turned off the light then you left.You should use past simple tense in this sentence.

Answer 2

I think it is possible to use present perfect in the context because we use simple past and present perfect for adverbials today , this morning etc.

I have met my friend today.

I met my friend today

Both the sentences are correct.

So,I think both present perfect and simple past are correct.

I have turned off the light before leaving this morning

I turned off the light before leaving this morning.

Since the speaker is speaking in the morning, present perfect is not wrong.

I think the above two sentences are correct.

Besides, the OP is saying that he was speaking this morning.

Here is the link which shows the use of present perfect and simple past.

https://www.grammaring.com/present-perfect-with-an-incomplete-period