Both tabulates and rugosans evolved independently as part of the Ordovician Radiation; the tabulates appeared first in the Early Ordovician (~488 Mya), followed by rugosans about 20 My later.
2013, Walter M. Goldberg, “A Brief History of Reefs and Corals”, in The Biology of Reefs and Reef Organisms, Chicago, Ill., London: University of Chicago Press, section 13-2 (An Introduction to Paleozoic Corals), page 272, column 2