According to Facebook's current documentation, the Stream URL and Key are valid for 7 days. Once you preview the video (start the stream in OBS and preview on their end), you have up to 5 hours to go live.
If you close the Facebook Live dialog and open a new one, your old stream key will still "work" in this time period, but you will not be able to preview it in their dialog, so you will not be able to actually go live (Facebook requires you to preview the stream and indicate that you're going live by clicking a button on their system before actually going live). I'm having trouble finding info on how Switchboard/Joicaster relate to this problem. Could you elaborate a bit on how you would set up OBS once for Facebook Live?
Another thing to mention is that the Facebook Live stream are created through the Facebook API. You only have to link your Facebook profile and select the pages Joicaster/Switchboard can access and it creates the live event automatically when you click on "Start Broadcast".