文档上写的好玄乎:

https://w3c.github.io/resourc...

The startTime attribute must return a DOMHighResTimeStamp [HR-TIME-2] with the time immediately before the user agent starts to queue the resource for fetching. If there are HTTP redirects or equivalent when fetching the resource, and if all the redirects or equivalent are from the same origin as the current document or the timing allow check algorithm passes, this attribute must return the same value as redirectStart. Otherwise, this attribute must return the same value as fetchStart.

这个时间具体的计算方式是什么?