I check my call duck eggs twice a day; morning and evening. Twelve hour after internal pipping occurs, any eggs not externally pipped get punctured on the air cell end. I do this as I have learned that not doing so cost me the lives of some ducklings. I assist to get the best possible hatch with short billed calls. With my last hatch, one duckling was lost as I waited too long, but ended with 12 healthy ducklings, all of which needed help to hatch.
However, whenever you open your incubator the humidity changes, at the worst time. The change could cost you. Humidity changes can and do make it harder/or impossible to hatch as it dries the membranes. For me, that does not matter as all the eggs are assisted. Over a period of 50+ years, assisted hatches are easy and my wife and I very rarely lose a baby.
I would not tell some one to candle when the hatch date is so close as this could cause them problems and possible losses.