In the file Timestamp.php there is a bug in how the timestamp should be displayed. It says:
const DATE_FORMAT = 'Y-m-d h:i:s';
but shouldn't it be the following
const DATE_FORMAT = 'Y-m-d H:i:s';
Note the upper case H.
If you use lower case, then it's 12 hour format and you have to use AM/PM, but that's not appropriate for some non english languages (eg. Swedish). So please change to upper case H.