date/time format

Certainly possible. Where are you seeing this exactly? In the rendered node?

Confirmed, module isn't respecting site time format. I have time set up fo 24h format, but this module shows time slot in 12h format in rendered node. Can this be changed?

hmm, I don't recall why, but seems like it's hardcoded in function _timeslots_signup_form($node, $admin).

e,g,:

    $form['timeslot'][$slot]['start_time'] = array( 
      '#value' => format_date($data['start_time'], 'custom', 'g:i a', $node->start_offset),
    );

Thanks for a hint. I just changed "g:i a" (12hr time schema) to "G:i" (24hr time schema). I found three places, where this has to be changed. No problem,