We recommend spending at least 7 days in Greece, so you can easily explore the major mainland destinations like Mykonos, Santorini, Athens, etc., as well as some of the famous Greek islands like Ios, Corfu, etc. If you have some more time, you can even look at 14-day Greece holiday packages, where you can spend a week exploring the mainland and head off to the seas, exploring the Greek Islands during the second week.