I just found that when I change the startup poller from the default "JBoss 7 Manager Service" to "Web Port" the initial delay is gone. The JBoss EAP 6.0 Runtime Server seems to have the default at "Web Port".
Before a server starts up, we do one "poll" against it, basically to see if an instance is already running. If an instance is already running (either launched outside or eclipse or somehow was never shutdown), we present the user some options on how to handle this... such as launch anyway, or cancel since a server is already up.
To perform this poll, we use the poller you have selected in the server editor. It would appear that attempting a management connection to a nonexistant server takes longer to timeout than making a web connection.
The problem here is that we in past had many users report port errors etc. because they had other servers running.
We added thus a pre-launch check to see if mangagement port or webport responded and warn in that case.
That check when using management API seem to be slower than we would like. We'll look into what we can do to fix/improve that.
For now, using the web port is best workaround.