Nope, you can still steep it further. Honestly, unless you have tons of alcohols in your vape to evaporate off, you don't HAVE to steep with the top off a long period of time. I use distilled water in my mixes, so if I'm breathing them, it's usually for short periods of time. Leaving cap off for too long can also degrade the flavors a bit. Like everything, it's something of a tradeoff. Now that I am mixing steadily, I like to let my flavors steep at least a month, and so mix accordingly. I don't shake them every day, but every so often nor do I breathe them every day. Mainly, I just let time do its thing. Whatever you wind up doing, write it down so that you can see how you like what you did and have repeatable results.
Far as I'm concerned, nothing beats "time" for steeping, although there are tons of other methods, (ultrasonic cleaner, hot water bath (not scalding) mixers and agitators, and etc. But if you have time on your side (I do) there is no need for all that and I don't find that it would overall improve my experience, I just like to let nature take its course and 95% of the time, I am doing nothing other than let them sit, shaking occasionally (and vigorously).
Best of luck,
Anna