It means both “Hello!” and “Goodbye!”. You can use it any time of the day. This greeting is informal, but using the plural “Γεια σας!” will make it sufficiently polite.

It means “Continue well” and is a recent addition to the spoken language. You can use it in any case where people will stay behind and continue what they’re doing, as opposed to leaving at the same time with you.

Have a nice afternoon! You can use “Καλό απόγευμα” in the afternoon, until early in the evening.

Have a nice evening! We say it until late in the evening, until about ten. After that, we’d say “Good night!”

Good night! We say “Καληνύχτα” when we leave for the night. It can be used until after midnight.

Before dawn, you’d use “Καλό ξημέρωμα!” It refers to the daybreak.

Farewell! You can use this greeting when you leave for good or for a very long time. It has a permanent ring to it. In any other case, you can simply say “Γεια σου!”. Saying “Αντίο” when you finish work or leave a shop sounds a bit old-fashioned.