Not really, but once they start laying, the nest will be soiled and thats not nice either for you or the chickens - thats why blocking off access to the nests - particularly on a night time is important.
CT
There maybe a few things to consider.
1.Make sure your roost is higher than the nesting boxes
2. Block off the nesting boxes for now, as they are not yet laying
3. They may need a bit of encouragement to use the roost - try putting them on the roost once its dark
Young chickens, if they have...