Jackson makes a clear timeline: 5-10 million years ago, atlantis left. the ancient empire was already destroyed by the plague by then.
if the Destiny is a billion lightyears from home, (10^9 LY's,) , then it travelled a meagre 1000 Ly per year. it would take 1000 years for Destiny to travel across the Milky Way. amp it up with a factor 10 and we got 10^4 LY per year. well, that's a decade for the MW. which is an incredibly long time. even the goauld didn't need that long, and they seem to use pretty old stuff. still, we're talking averages. we don't know how long it takes to refuel. so this is the average speed. still, it seems quite slow to me.
but if it's just a few billion lightyears away, a million years of age fits closer than 10k years. so, was Jackson wrong then?