well seeing as genesis tends to do the planet forming thing quickly thats likely not as mush of an issue as traveling a considerable distance and not only still having the energy to reform Regula but to do so before Spock dies from radiation poisoning.
Besides the view of the Genesis planet makes it look like the planet is just forming since it looks like magma is floating around it.
You know, I can accept that the Genesis Effect can cause (plant)-life to spring up pretty fast, or the release of gases that form an atmosphere which in turn, over time, will change the planet's surface.
But I can't accept that this thing can scatter a nebula then pull it together so fast, so violently that it forms a planet which then cools down within minutes.
Genesis as a central plot-element, and as it was presented in the video is far fetched enough with its ability to create life. The idea that it can speed up the processes that create planets (accumulation of mass, pressure, heat, cooling down) is too far out there for me - yes, even with Trek's matter-transporters, warp-drives...