I find that fruit type juices need very little steeping, usually good to go within 24 hours.
Dessert and more complex flavours do take time for the flavours to develop.
Try it again after 7 days.
If its good, then just make a 30ml batch every week or two, that way you will always have some fully steeped and ready to vape.
If its still doesnt taste right, give it another week lol.
Also if it tastes bland, it may be worth adding another 1-2% flavouring and u guessed it, wait another week lol
You soon get used to mixing well ahead of time you want to vape it.
Good luck