I always steep tobacco flavors for one week using the traditional method; I leave the tightly sealed bottle of e-liquid in a cool dark place -I use a drawer in my bedroom. Once a day I take out each bottle of steeping e-liquid and shake it vigorously for 15 or 20 seconds and then put it back in the drawer.
Some uncap and leave e-liquids overnight -or longer- and then continue storing them in a cool, dry, dark place.
Still others prefer some type of hot liquid bath as gregmc3 has suggested.
After reading about steeping in the e-liquid DIY thread I agree that tobacco flavors should always be steeped. I also have read many accounts of those who purchased (or made) a dissapointing flavor only to steep it (the traditional way) for a week and when they return to it they like it.
I recently purchased what I consider to be some upgrade e-liquid. It had a date on it. Other bottle may say "Born On" with the date or some other phrase. This is so the buyer knows that the e-liquid has (or has not) been steeped when they receive it. They can then use at will or steep if they want to.