Talking about past!

Would someone explain to me which one is correct?

He spent one hour telling me why he is so busy and cannot do that.

or

He spent one hour telling me why he was so busy and could not do that.

Or maybe both are true? conveying different meanings?

Thanks, cheers!

I am talking about an event that took place last week during which I had a conversation with a friend.

In the first variant, he spent that one hour and told why he had been busy before that event, and therefore, he could not do what I had asked from him.

He told me, "I was so busy and could not do that"

In this case, I think I can say:

He spent one hour telling me why he had been so busy and could not have done it.

In the second variant, He simply told me that he could not do that due to his busy schedule.

He told me "I am too busy and can not do that"

He spent one hour telling me why he was so busy and could not do that.

but in some cases for example, if it happened not far ago, I can say it in the present tense.

Today, he spent one hour telling me why he is so busy and cannot do that.

just wonder how far ago that can be.