Green juice is very alkalizing, so I guess you wouldn't want to drink it after you eat something large. I'm guessing it would just alkalize the stomach acids a little and give worse digestion for the food you ate.

When is the best time to drink a green drink/green juice?

Also, how long does juice/liquid stay in the stomach? I would assume you would not want to eat anything until after the juice has left your stomach?

Water will clear the stomach in about 10 minutes. (It is a sound idea to start the day with a glass of water to flush out the system )
Fruit juice as it contains sugars needing digesting will take longer, but not a great deal longer as they don't contain fat. Should clear the stomach in an hour at the max.
So its fairly safe to say your green juice will take about the same length of time.
Before breakfast is the time I would suggest being best.

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