google script to track time that a card in 'done' spent in a 'doing' list on a trello board. you need an api key, a token and a google spreadsheet. you can run this script as frequent as you want using the trigger that google script offer.

trello_time_track

function trelloFetch(url, extra_params) {
  var key = [your_api_key];
  //how to get a token de https://trello.com/1/connect?key=[your_api_key]&name=[name_for_token]&response_type=token
  var token = [your_token];
  var authSufix = "key="+ key + "&token=" + token;
  var completeUrl = "https://api.trello.com/1/" + url + "?" + authSufix;
  
  if (extra_params != undefined){
    completeUrl += extra_params;
  }
  
  var jsondata = UrlFetchApp.fetch(completeUrl);
  //console.log(jsondata);
  var object = Utilities.jsonParse(jsondata.getContentText());
  
  return object;
}


function getCardsFromDone(){
  var list_id = [id_of_your_done_list];
  var url_cards = "lists/" + list_id +"/cards/all";
  var cards = trelloFetch(url_cards);
  var card_events;
  for (var i=0;i<cards.length; i++){
    var url_cards_events = "cards/" + cards[i].id + "/actions"
    card_events = trelloFetch(url_cards_events,"&filter=updateCard,updateCard:desc");
    var active_times = [];
    for (j=0; j<card_events.length;j++){
      if (card_events[j].data.listBefore!=undefined && card_events[j].data.listBefore.name == [your_'doing'_list]){
        var tf = card_events[j].date;
        continue;
      }
      if (card_events[j].data.listAfter!=undefined && card_events[j].data.listAfter.name == [your_'doing'_list]){
        var ti = card_events[j].date;
        var active_time = {ti: ti, tf: tf};
        active_times.push(active_time);
        continue;
      }
    }
    cards[i].active_times = active_times;
    continue;
  }
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getSheets()[0];
  var baserow = 2;
  var basecolumn = 1;
  var row_counter = 2;
  var one_hour=60*60*1000;
  for( var i =0;i<cards.length ;i++){
    for(var j=0;j<cards[i].active_times.length;j++){
      var project = cards[i].name.match(/[^\[\]]*(\[.*\])?[^\[\]]*/)[1]
      var estimated = 0;
      if (cards[i].name.match(/\((\d+)\)/)!=null){
        estimated = cards[i].name.match(/\((\d+)\)/)[1]
      }
      if (project != undefined){
        sheet.getRange(row_counter, basecolumn).setValue(project.toUpperCase());
      }
      sheet.getRange(row_counter, basecolumn+1).setValue(estimated);
      
      sheet.getRange(row_counter, basecolumn+2).setValue(cards[i].name);
      var ti = new Date(cards[i].active_times[j].ti);
      var tf = new Date(cards[i].active_times[j].tf);
      sheet.getRange(row_counter, basecolumn+3).setValue(ti);
      sheet.getRange(row_counter, basecolumn+4).setValue(tf);
      
      var diference = (tf.getTime()-ti.getTime())/one_hour;
      
      sheet.getRange(row_counter, basecolumn+5).setValue(diference);
      
      row_counter ++;
      //var counter = sheet.getRange(1, 9);
    }
  }
}

it assumes that there is only one member per card, some extra development is required to take in account cards with more members.