Is harvest time important for coffee quality? The other day, I spoke to a tea fanatic. he introduced me into tea world and also explained me, that harvest time of tea leaves has significant role in tea quality. (Especially the first flush which is the first harvest in given year)

It made me wonder: Is there any significance to coffee quality regarding the bean's harvest time?
Yes, it does, but it's much more complex than that :-)

Harvest times vary greatly depending on the latitude, altitude and variety of beans being harvested. There is a very large table here which illustrates the variety of harvest/shipping seasons, as well as the optimum points of both.

In general, December-February is best, but some countries vary anywhere from June to October. Some countries with a larger variety of crops have a lot of different 'Best' points, e.g. Kenya:


(The top brown/red line indicates harvest times, Red Bs indicate the optimum harvest times.)