If I were to say, "Let's meet for lunch about noon. We can take about an hour for lunch." you would say, "I waited a whole hour for you. Where were you?" It's not a specifically designated hour, but an approximation.
If I were to say, "Let's meet for lunch at noon. I get an hour for lunch." you would say, "I waited the whole hour for you. Where were you?" It's a specifically designated hour.