Timing

• Queueing. The browser queues requests before connection start and when:
  • There are higher priority requests.
  • There are already six TCP connections open for this origin, which is the limit. Applies to HTTP/1.0 and HTTP/1.1 only.
  • The browser is briefly allocating space in the disk cache.
• Stalled. The request could be stalled after connection start for any of the reasons described in Queueing.

See:

Network features reference  |  Chrome DevTools  |  Chrome for Developers