I generally bang the humidity right up as soon as I move the eggs into the hatching tray, three days before due date. Have just moved a batch on Monday, most of which I could hear cheeping: all are now pipping, and I tend to spray them with a garden mister spray (water with a tiny bit of incubator disinfectant in it!) every two to three hours to ensure that the humidity doesn't drop below 50%. One of the best investments that we made two or three years ago is a digital temperature/humidity reader! Keep the humidity ideally between 60-70%, but not below 50, and you should be OK. Don't forget that from them starting to pip to actually hatching can take a couple of days - mine aren't due till Friday, and are merrily pipping away!!
Good Luck with the hatch - fingers crossed.....