I have a webserver running on UTC. The date fields are saved as UTC. The user has a timezone of 'Europe/London' (UTC+1h). All the countdown dates have 1 hour added to them.
around line 226 in jquery_countdown.module the date field stored as UTC is formatted using the date() function with a hardcoded offset of +0000.
$vars['id'] = $instance['field_name'] . '-' . $instance['id']; // use field as unique id
$vars['options']['until'] = date("F d, Y g:i a +0000", strtotime($item['value'])); // get date from start field
To fix this bug i guess it needs to pull the timezone from the user object and apply the correct offset here.
Will attempt to supply a diff patch when we're off deadline