If you are following the same definition for both—i.e., nautical twilight and nautical dusk—there will be no overlap between the two. However, if you are following mixed definitions—such as nautical twilight and civil dusk—then there is technically some overlap and it could be said that nautical twilight and civil dusk occur simultaneously for a period of time.
If you are following the same definition for both—i.e., nautical twilight and nautical dusk—there will be no overlap between the two. However, if you are following mixed definitions—such as nautical twilight and civil dusk—then there is technically some overlap and it could be said that nautical twilight and civil dusk occur simultaneously for a period of time.