TL;DR: It is fine to have green tea at night before going to bed. As my answer explains below, drinking green tea is good for health in general and not just before going to bed or any other specific time.
You can drink green tea at any time of the day or night. Tea in general contains less caffeine than coffee and other drinks such as Coke, Redbull, etc. and should not impact your sleep much (unless you are highly sensitive to caffeine).
Green tea contains relatively lower amounts of caffeine even in comparison to other teas (for e.g. black teas) and is considered beneficial to health due to the presence of antioxidants and other minerals in it.
We also highly recommend using loose leaf tea to brew your tea if you plan to consume green tea regularly. Teabags almost always (95%) lack the depth of flavour and nutrients present in loose leaf tea.If you’re looking for a great everyday green tea, check out one of our favourite green teas: The Jade of Bengal | Darjeeling Green Tea