Every so often I'll purchase a so called "premium" juice everyone seems to be hyped up about (Usually in a 15ml bottle). What I do is split it into my 3ml bottles, which in turn gives me 5 bottles @ 3ml each.
The first bottle I vape off the back, second usually after 3-4 days of steeping(aging), third after a week, forth after 2 weeks, and fifth after a month.
Imo "most" juices tend to get better after 2 weeks, and after 3 seem to have little taste difference thereafter. But keep in mind that is from personal experience, with the limited juices I've tried.