David Stern, "Midrash," Contemporary Jewish Religious Thought, ed. Arthur Cohen and Paul Mendes-Flohr (New York, 1987) 616-617.
The tannaitic collections, called after the tannaim, the sages who lived between 70 C.E. and 220 C.E...
...the amoraim, the sages who lived between 220 C.E. and the end of the fifth century...The major amoraic collections, edited between the late fifth and eighth centuries...
These are good dates for me to know.