In Ben's first fight with the mummy creature, the full moon appears all over the place. It's especially incorrect that a full moon should appear directly above dawn's first light, or that the light of dawn should come well before 5:00AM.
Grandpa Max makes a number of deductive and informational leaps without facts or experience to back it up, such as knowing the cows and the security guard weren't exposed long enough to the corrodium for their monstrous transformations to be permanent, or that no one need worry about the animated mummy wrappings (which aren't alive to start with) coming back to life if buried under concrete.
No explanation for how the mommy monster (mere animated wrapping that form a man-like shape, powered my meteoric energy that presumably came to Earth tens of thousands of years ago) should come into being to bother people only in modern times.