This fight can feel a bit awkward as a Mistweaver with the differing time portions and requirement to burst heal the Time Release mechanic. Depending on how high your raid stacks Power Overwhelming, you can get some good use out of Essence Font and Mana Tea during this time, as well as Chi Burst as the raid should be stacked while Power Overwhelming is going on.
In Mythic difficulty, the most difficult mechanic to handle as a Mistweaver is the fast Time Release mechanic. Ideally, you will have a charge of Thunder Focus Tea available and can use an instant Enveloping Mist. It’s also sometimes useful to let your Sheilun’s Gift stack higher than you might otherwise to get some burst healing when needed. Otherwise, Vivify under Uplifting Trance can be used to good effect.