I know I'm a million years late for you but I just installed this plugin and came up with the same problem. Here's the fix:
Ok look for:
// setup jocker date range
Under that I believe it said:
$tm_time = "2%-".gmdate("m-d")." %:%:%";
Or something similar? Change that line to:
$tm_time = "2%-".date("m-d")." %:%:%";
Now look for:
function time_machine($args) {
(This should be a little above what you just were working on)
Under that add:
date_default_timezone_set('Canada/Eastern');
Now where it says "Canada/Eastern" enter the timezone you are in (list is here: http://www.php.net/manual/en/timezones.php )
Ideally I'd want this to show based on the time zone of the reader, however I didn't drink enough coffee today and I just got out of yoga so my mind is kind of mush. This makes it related to the time zone you set.
Hope it helps.