Groupchat: Show subject timestamp in preferred format

%c uses the preferred format on the current system
3 jobs for master in 2 minutes and 49 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
passed #13587
run-appdata

00:00:06

passed #13586
run-tests

00:02:33

 
  Build
passed #13588
run-build

00:00:10