So it takes as little as 2 hours and up to day for your course to be created and students to appear in it.
As students register for a CRN, they are added to the Blackboard course associated with that CRN, and as they drop they are made "unavailable" to that blackboard course, but not removed. Several times a term including before the first day of classes and immediately after Add/Drop period we automatically REMOVE all the students who had dropped the course. This removes the students that the system had made unavailable. Since automated enrollment continues throughout the term, do not attempt to remove a registered student from your roster - they will simply be put back in later that day. However rest assured that if the student has dropped, they will not be able to access the course since they will be "unavailable" to it.
Students frequently change sections and courses before settling on their final selections. During this time they may also be submitting work and taking tests. If they are deleted from the course, all this work is lost. So we wait until the dust settles and the add-drop period is over before deleting the "extra" students. Making them unavailable to the course prevents them from accessing the material, but if they re-add the course their previous material will still be available.
In this way Banner and Blackboard, and the Course channel on MyWestern are kept synchronized.