You can drink green tea at any time of the day, however be mindful that it contains caffeine, so if you have it in the evening, it may keep you awake. If you’re particularly sensitive to caffeine, then you may want to stop consuming green tea prior to the mid-afternoon mark, so that the effects of caffeine have time to wear off before bedtime.
If you aren’t particularly caffeine sensitive, then green tea is a great palate cleanser after dinner. It’s also said to have benefits for your teeth and gums, which is useful after a meal, so feel free to have it in the evening, and perhaps just brew it a little weaker.