The tweet says that the Galaxy S II will land at retailers in April. The specific launch day isn’t offered, so it could be any time now. What we still don’t know is which areas will get what processor. Samsung will use the Tegra 2 chip inside some units and its own Exynos A9 in other areas.
Both of the chips will be clocked at the same 1.2GHz speed. The original clock speed of the processor was set at 1GHz so the 0.2GHz speed bump is a nice addition. I would assume it won’t hurt battery life too much or Samsung would have left the clock speed alone.