If Greece has made that decision, it doesn't make a lot of sense. Cases are surging, as are deaths. Why wouldn't you lockdown completely till Mat 14th and then accept visitors? And I'm saying this as someone in the UK who knows that if things continue the way they are going in Greece, they'll be getting no UK visitors, who make up a large portion of visitors every summer, because the UK government just won't allow us to come.
Worst case it's amber and you need to quarantine on the way back. That's the question, will they be amber or green.