grammar - Has/have been vs was/were

I understand we should use has/have been for something which started in past and still continuing in present. But is it right to use for something which started in past but has just completed or completed a few hours ago?

For example - I want to tell someone in what I did the whole day. Should I say - I have been in meetings all day or I was in meetings all day? May be I should use "was"? Because day is already over? Please suggest. Thanks.

• Next grammatical number - Does the plural include the singular?
• Previous grammaticality - Is using the possessive 's correct in "the car's antenna"?