I didn't have/haven't had the time to....

Either. Grammatical form expresses meaning - as you say. Here both meanings match a possible view of the event, and so both could be used. The choice is up to the speaker.

You never choose to use a grammatical form. You choose to express a meaning - and then use the grammatical form which expresses that meaning.

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Yes - this is another situation that shows that it is up to the speaker to choose the meaning s/he wishes - either that the words belong to the past, or that they have present relevance. Here are some examples from Google :

As Perry has said before, our comic is not dead.
As my mom has said, when one person is unhappy, it usually means two people are unhappy
COMPARATIVE law, as Professor Wigmore has said, is a convenient but loose term.

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