Rule for duration of staying outside USA

[immihelp]

Dear Reader:

I am an American citizen. Currently I am in Athens, Greece.Before my 3 months visitor visa expired I obtained a 6 month extension to stay in Athens. If I wish to stay another 3 months, and don't want to try and get another extension, can I leave the EU for a day and come back in with a new 3 months, or do I have to leave the EU for a longer period of time.

[immihelp]

There is no rule regarding how long you need to stay outside. However, if you try to stay too long, you may be violating the purpose of your visit and may be difficult to get entry into Schengen area again.