Well, I don't know the answer off the top of my head, but I can suggest how I would try to figure it out, if this was something I needed to do.
First, I'd be looking in the mod_form.php for mod_bigbluebuttonbn to find the field name in the mdl_bigbluebuttonbn table that represented the 'due date' field.
Then I'd look through the code that handles the moving of activities in a course (I think it's course/rest.php, but I've not spent long looking) - if you trace through there, you should find a function you can call to move an activity to a new location in a course.
Then I'd probably put together a local plugin, with a function that looked up all the mod_bigbluebuttonbn activities in a particular course and moved them to new locations, based on their 'due date' field.
This local plugin function would then need triggering in some way - it could be a scheduled task (to run every day, every hour, every minute?), or it could be a CLI tool that an admin could run, or you might want to put together a UI to trigger it.