The response to a /meta/subscribe message is delayed in case a /meta/reconnect response is currently pending.
If no /meta/reconnect response is pending, the /meta/subscribe is returned immediately.
The delay only happens with the JSONP transport but debugging through the code I can't see any reason for that delay.
The transport.complete method is called at the end of the /meta/subscribe request and even an explicit _out.flush() is executed there.
However the response is only returned at the same time the /reconnect times out.
Same is true for for unsubscribe and I haven't tested publish yet.