Avatar not shown and Short time format want

In conversations, Avatar is not shown for members other than Administrators.
In Last message table, I don't need time.

Please help.

Avatars are grabbed from the _users table. Double check if these users have an avatar set, and if they don't, I suggest you to use a default avatar plugin such as Letter Avatars 1.0.2.

As for the time, that row uses the my_date("relative") format, which uses both date and time. If you want just the date, you can find in inc/plugins/symposium.php, line 789:

$date = my_date('relative', $conversation['lastdateline']); 

And change it to:

$date = my_date($mybb->settings['dateformat'], $conversation['lastdateline']); 

Beware though, this will strip off the "Today" and "Yesterday" labels.