I think the consensus here has been a 100-hour burn-in, while 72 hours is recommended from Ken Ball (I think).
I heard the fully-burned in demo ones at CanJam, and heard an immediate difference when I started using my brand new ones. The bass is a lot more refined on the demo ones, but that was just my quick impression at the show.
In the short burn in time I've had so far, the bass is already much more refined and the soundstage is naturally wider and more detailed much more quickly... if that makes any sense. At first it'd take a while for me to get fully-immersed and appreciate the clarity, but now it's almost immediate, and it continues to improve.
Some here have said that burn-in with the Vega is more noticeable than most other IEMs or devices, and a frequency chart showing the differences in a new pair vs burned in ones was provided either by Campfire or another member at some point, I forget who.
And please forgive if I use the descriptive terms inaccurately, I am still a noob