It seems to me that if you posit a "god" wholly within time, then time is itself greater than that "god" -- IOW is the real "god", unless of course there's something even greater than time.
I believe the physicists who busy themselves with such things maintain that time began with the universe (some at least say it's not constant) and that it is, in fact, the fourth dimension -- like height, width, depth. Sub-atomic physics, so I hear, requires many more dimensions to account for/explain the quark.
Physics makes me dizzier than theology . . . ;-)
I found Whitehead unsatisfactory for other reasons, but, yeah, I think you're pretty much right.