I launch the dedicated server out of Blockland (start game then etc.)
That's not dedicated
do I need to stay in Blockland or can I exit?
Leave the black console window open
When you installed v20 it gave you an option to create a dedicated shortcut.
If you choose not to, you just need to create another shortcut, with the target ""C:\Program Files (x86)\Blockland\BlocklandLauncher.exe" -dedicated -map mapName"
Change file path to the path to your launcher, and mapName to the name of the map you want.
Alternatly you could just copy your existing shortcut and add -dedicated -map mapName to the end of the target