well i doubt harry went relatavistic there, his brain would exploded from the mass change. A person's awareness of time can be changed via medical means, in effect Lash just 'overclocked' his computer.
Uriel is a different issue; for beings made netirely of soul stuff (like he and harry were at that point) time becomes entirely subjective.
and yes, I believe in the present. Time may be quantum- and thus at some point indivisible- ive read articles about that possibility in scientific american. Then again it may not be. heck, it could be 'holographic'. its one of the great mysteries of modern science.