Nah, I think this will be fine for us. Many fights are not 6+ minutes, so the 30 extra seconds is almost another bloodlust for us, making it almost on par with the mage's ring. And honestly, I'm fine with another class getting something good. Let's not hate on Mages because the grass is greener on the other side.
Well, let's clarify this a bit:
At 00:05 somebody else in the group does Bloodlust
At 00:45 that Bloodlust expires, and the mage casts Time Warp
At 01:25 his Time Warp expires
At 5:45 his own Time Warp is off cooldown, and he can cast it again. The fight needs to be 6:25 minutes to take the full effect of the third Bloodlust.
It is for sure a very strong legendary, and you should be happy if you meet a mage who has this
And then feel sad for him, if he doesn't have another class in his group who can do BL, because then the effect is almost useless for him unless the fight is 5+ minutes long.