Warmode Assassin upgrade criteria ?

According to the "Soldier of the Horde" buff you have to get 10 kills without dying to upgrade to an Assassin for a 15% damage & healing buff. Then if you continue killing people you get a bounty on you.

Is there a time limit ? Do i need to get the 10 kills in a set time frame ?
Do I need to get the killing blows or just help kill them ?
Do environment kills count (knockback & dismount falling damage or npc stealing the killing blow) ?
Does the counter reset on changing zones ?

Doing Darkshore Warmode Pvp, died twice early on then went on to kill 25-30 people before finally dying but never upgraded to an assassin.

During this time 3 Alliance bounties were announced and killed so the system is obviously working just wondering what the specifics of it are.