Quote Originally Posted by Serneum View Post
Not entirely true. I can usually have my Sentinel up a few seconds before the next double Wicked Wheel. It's not a guarantee, but it is possible to do, even with really high DPS.
After the initial sisters phase, Garuda transitions into the next phase after a certain amount of time or when she reaches 55% HP, whichever comes first.

Therefore, the duration between the first two sisters phases varies, depending on how much DPS you have. You might have Sentinel barely before the next Wicked Wheel, but someone else's group might have better DPS.