tweak handling of slow/missing upstream

our fetch and render timeouts were both 20s, causing the 'finish early' event to fire immediately before the upstream timeout turns it into a 400.

This moves the upstream connection timeout to 10s, meaning unavailable servers will hit 400 instead of 'working...'.

I also removed the 'Fetched...' timing diagnostic message when the fetch fails.

and switched the HTTP status for the working... message to 202: Accepted from 200.