Fruit flavors generally don't change very much, if at all, and are great right out of the gate. The Cookie Monster will probably develop the vanilla tones more over time and will get better with steeping.
I bought 30 ml of CM the other day, FV is about 20 minutes from my house, and am letting it develop now. If you like their
juice you should visit their shop if your ever down this way, great group of people.