In the UK at 12.01pm it's afternoon. People are precise about it. In Spain afternoon arrives in a much less predictable manner - it becomes afternoon sometime around 2pm but I've been told that it's often driven by whether you have eaten or not. I have eaten so I say "Good afternoon" you haven't so you reply "Good morning".
In regard to the seasons though the Spanish are very precise. For days there have been little mentions on the news channels, as they hand over to the weather forecasters, that we're approaching the beginning of Winter - "Soon be winter yet temperatures set to rise!"
The credits for the weather bulletins on the State channel include a little caption that says what season we're in. I noticed, when I saw a weather forecast attached to the midday news, that it was still Autumn. I was surprised because I thought the 21st was Solstice and that we passed into Winter. My answer came on the 3pm news, the caption said Winter - "We passed into winter at just after 1pm today." said the weather chappie and he had some satellite pictures of the World and some nice snaps of the South Pole to show us how the solstice worked.
Off to Culebrón today so new posts will be there for a few days.