Nest box questions...
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A lack of interest in the nest prior to the onset or production is not unusual - it is as they approach that first egg that they start to investigate potential places to make a suitable nest.
That being said - there is no way to know whether the nest you have provided will be what they are looking for until the time comes. They may lay on the ground, in the floor of the coop, in the nest - or who knows where. You can make the nest more attractive by making sure it is a good potential nest from their perspective -- hens like privacy and security. Perhaps you can take a photo or two of your setup and post them so that we can see what your girls will see so we can better help you understand if the nest you have will be one likely to attract them. You can also "bait" the nest by placing golf balls, wooden eggs, etc in it to indicate to them that another hen has already found that site to be a good place to lay her eggs. This works off the natural instincts that often lead to having several nest boxes but finding all the eggs for a given day in one nest - and seeing hens lined up waiting for someone to get out of that nest so they can get into it to lay their egg vs. using one of the other empty nests.