It depends on the supplier. I mean, if it's imported from china, it's been steeped in a warehouse then on the way to the supplier in another country, then sat in their stock for a while. Steeping that is like waiting for wine to turn into vinegar.
Some suppliers make theirs and it can take time to settle. Normally you'll get a flowery/perfumy smell if it really needs it but not always. Some flavours just need time to blend as well.
Rule of thumb: if it tastes good on day one, vape it on day one. If it doesn't taste good on day one, let it sit for anywhere from two weeks to a month and if it still doesn't taste any different it never will. Except this one cappuccino flavour I have that's a year old, it tastes like corn chips now
