If you dried for 18 days at 60/60 with ample air movement, and your weed is in the jars at 57%, then you're probably good to keep them in there without having to burp them. But I'd still open the jars every few days to smell them to make sure. They might slowly come back up to a higher RH than what you want, so just monitor that humidity gauge in the jar and make sure. I don't see how they will go over 60% RH if you've already dried them at 60/60 for 18 days, but I don't know what the bud density is or the thickness of the stems, size of the plants, etc. ....so it's just a guess based on general information.