Gravity measurably affects the passage of time for observers at different gravitational potentials. So a clock at the centre of the Earth would run slower than one on the surface. But the early Universe was almost perfectly uniform, so while it was extremely dense, the gravitational potential was equally close to being uniform and so there was no time dilation.

Not necessarily, because the restrictions they described would still exist: lithium would still be incredibly scarce, and the conditions simply aren't extreme enough to get the triple-alpha process running, counter-intuitive as that may sound. The problem here is that fusing two ^(4)He nuclei produces ^(8)Be, which has an astonishingly short half-life of one ten thousand trillionth of a second. Only inside the core of a massive star is the reaction rate high enough to fuse a third helium nucleus to make stable ^(12)C before the ^(8)Be falls apart.