I like you second alternative better than the first. Look at Peris hotel. Its about a 15 minute drive from the airport and they offer free shuttle service. Of course if you have a big budget you can stay at the Sofital which is at the airport. As I see it you have a total of 9 nights in Greece. So that is night 1.
Next morning fly to Santorini.
You might consider an additional night in Santorini. Flying on the 17 and returning on the 19 is really only a day and a half in Santorini.
You will still be jet lagged so spend the extra day relaxing and taking in the views. So that is night 2,3 and 4.
Now fly back to Athens and rent the car from the airport and drive to Delphi. This should allow you to arrive in the afternoon. Find a hotel, wander the village take in the amazing view down to the gulf of Corinth visit the museum and if you still have time visit the lower site. That is night 5
Next morning get to the site at opening. You will have it virtually to yourselves for at least tow hours until the tour buses arrive. Then you will be way up in the site and it will take about another hour before the crowds reach you. Leave by noon and drive to Meteora. Time you arrival late afternoon or better yet early evening. At this time the monasteries will be closed and the crowds will be gone. Take your pictures then because next day the tour crowds will be everywhere. Night 6
Determine which monasteries will be open the next day and get to at least the first one before the tour bus crowds arrive. This can be a long day so you might consider two nights at Meteora because it is a 5 hour drive back to Athens. night 7
Olympia Delphi Meteora https://www.flickr.com/photos/stanbr54/sets/72157645469717811/
Drive back to Athens for the end of your trip. You now have 2 nights for Athens before your flight home on the 25th. Nights 8 and 9. This plan gives you one extra full day in Santorini plus everything else you planned. Sequence is very important. You initial plan had to many trips into central Athens. Keep it to the end,