I have some of those little humidity things. Over time, I can just do it by feel. I trim wet, and the buds are left out a day or three. If they feel the right "dryness" I will jar them for a couple hours and feel again to see how soft, or damp the buds now feel. If they no longer feel the least dry on the outside, and a soft damp feel, they are usually 80%, which is way to wet to jar. Back out on the drying rack. Once they dont have that soft feel through and through, and although not dry yet, feel dry on the outside, even after an hour or two of being jarred.
Not describing it very well, its just a sense of feel that I have backed up with meters. Once at the above stage, they are usually ready to jar and burp, and will be 76-69%. or so, and burping frequently and fanning new air into the jars. Burp down to 62%, done.
I stopped with the packets. No need. If I have fresh flower ready to smoke and I want long storage, seal a meal and freeze.