36three.js AnimationAction

.startAt ( startTimeInSeconds : Number ) : AnimationAction

动画运行起始时间，就是延迟多少s开始执行动画。
Defines the time for a delayed start (usually passed as AnimationMixer.time + deltaTimeInSeconds). This method can be chained.

Note: The animation will only start at the given time, if .startAt is chained with play, or if the action has already been activated in the mixer (by a previous call of .play, without stopping or resetting it in the meantime).

参考：
https://threejs.org/docs/index.html#api/animation/AnimationAction.warp
https://github.com/mrdoob/three.js/blob/master/src/animation/AnimationAction.js