Depending on what your goal is my friend.
-If you are trying to be at the top of your server, then you should do nine tails from the begining because of the extra EXP that you get from it.
-If you are trying to get the most out of it, i would suggest you around level 60, I personally starts joining nine tails around level 65, i can't be bothered with it at the start cause it's time consuming and not worth the time.

I wi* lasted that long sometimes for more rewards lol.. Server 2 nine tails dies in like 10 min or less

I'd say do at least 10-15 minutes of 9tails until you reach level 50, and then try to stay for the full event. Usually I just put on an audiobook or something to help stave off the boredom, but yeah, the event can really drag on. You do get more benefits the longer the event takes.

As andywswift mentioned, if you are aiming to be top, you should do it full from the beginning, though it's still 100% possible to be a top player if you don't do 9tails until later, just a little harder. This post was last edited by Amadeu at 2016-11-29 09:32 This post was last edited by Amadeu at 2016-11-29 09:32

at what level did you guys first time killed the 9tails,cause on my server the top players are level 63 and the lowest life we can manage to get was x5.

Haha we kill it whole 39-40 minutes. Mostly cos only 10-15 people do dmg. But so much exp, 1M(1000000) easily.