Drying honey from 19% down to 17.5% — dehumidifier room, fan over the frames, how long does it actually take?

Istria, late frames off six hives last week — a mixed autumn honey, plenty of it, but the refractometer says 19.0% on the uncapped bits and 18.4% even on the capped frames because we had a wet, humid September. I don't want to bottle anything over 18 and I'd rather be at 17.5 for safety. My plan: stack the supers crosswise in the small store room with gaps between boxes, run a dehumidifier plus a fan blowing across the stacks, and keep the room shut. What I can't find is a realistic timeline. Are we talking 24 hours or a week? Does it work better on the frames before extracting, or in an open bucket afterwards? And how often do you re-check with the refractometer — every day, or is that overkill? I don't want to overshoot and end up with honey that won't flow out of the frames.