Please answer a question about the following article about Apollo:

Homer pictures Apollo on the side of the Trojans, fighting against the Achaeans, during the Trojan War. He is pictured as a terrible god, less trusted by the Greeks than other gods. The god seems to be related to Appaliunas, a tutelary god of Wilusa (Troy) in Asia Minor, but the word is not complete. The stones found in front of the gates of Homeric Troy were the symbols of Apollo. The Greeks gave to him the name ἀγυιεύς agyieus as the protector god of public places and houses who wards off evil, and his symbol was a tapered stone or column. However, while usually Greek festivals were celebrated at the full moon, all the feasts of Apollo were celebrated at the seventh day of the month, and the emphasis given to that day (sibutu) indicates a Babylonian origin.

When were Greek festivals celebrated?
at the full moon