I have heard that some tobacco juices take even longer than a week to be their best. I never DIY juices myself, but I have heard from people all over that tobacco liquids that come from vendors that mix them up fresh for you (HEathers Heavenly Vapes for one) usually take anywhere from a week to a month of steeping before ALL the flavors bring themselves out. I can't comment on this myself because I use mostly fruit/coffee type flavors and after some warm water steeping and a good shake they are usually good to go, and don't change much over the next few weeks either way.
If It was up to me, and I was DIYing, I'd seperate my mix into a few smaller bottles, label them for 1 week, 2 weeks, a month, steep each as long as the label says, and try them after each one! Sure this takes forever, and doesn't answer anything for you now, but it seems to give you a good baseline to go off of.