To avoid this issue, the only thing you need to keep track of during the entire NW, is "Fighting Time".
At the end of any battle (or when you are about to leave), open the map window by pressing 'm'. Look of the top right to check of "Fighting Time" counter (NOT Battlefield Time, which is totally, a different thing). Whatever the timer displays after hitting the refresh button, that's all you will get. All you need to do, is to accumulate a total sum of 5mins of 'Fighting Time' during the entire NW.
Fighting Time only counts when you are engaged in battle, taking damage or dealing damage (indicated by: character icon blinking red).
Hitting towers in bridge battle counts towards fighting time.
Hitting guards/npc's counts towards fighting time.
Digging crystals or flag does NOT count towards fighting time.
Buffing up does NOT count toward fighting time.
A battle has to end before the end of nw for the fighting time to count.
Additionally, only one win is required (does not matter if you actually contributed to the win or were just running around naked, throwing flower petals around).
Alternatively, the fighting-time requirement can be replaced by capping 2 flags.
The above original information comes from PWI staff (been confirmed for more than 1year ago). As far as I know, I don't think Aga has changed any of the above significantly (if he even did, at all). Since I did NW on this server or any other pw server in particular, I haven't had any issue with the above.