Bypass the invisible barrier
Usually you have to wait 30 seconds to go to the first flag to capture. There is an invisible barrier to force you to wait. But you can bypass it.
Stay just behind it, and use the sprint ability. Now, force it and after 2 or 3 forcing, you are now in the RvR instance and you can capture the first flag BEFORE your enemy, you have an advantage of 30 seconds.