Ruby : Convert timestamp to date time in given json input

I have a JSON input. I would like to convert all timestamp (createdDate ,modifiedDate) to time in ruby. How do I do that? I tried below methods but dint work

characterList.each { |char| DateTime.strptime(char.try(:getEditInfo).try(:getCreatedDate),%s) }


{"characterList": 
  [
    {"editInfo": 
      {"createdBy": "testname", 
       "createdDate": 1503137795000, 
       "modifiedBy": "testname", 
       "modifiedDate": 1503137795000}, 
     "charInfo": 
      {"charid": "3434", 
       "charDesc": "3434", 
       "status": "ON"}
    }, 
    {"editInfo": 
      {"createdBy": "testname", 
       "createdDate": 1503137795000, 
       "modifiedBy": "testname", 
       "modifiedDate": 1503137795000}, 
     "charInfo": 
      {"charid": "3434   6", 
       "charDesc": "43dfdf", 
       "status": "ON"}
    }, 
    {"editInfo": 
      {"createdBy": "testname", 
       "createdDate": 1503137795000, 
       "modifiedBy": "testname", 
       "modifiedDate": 1503137795000}, 
     "charInfo": 
      {"charid": "4hr_SLA", 
       "charDesc": "sd", 
       "status": "ON"}
    }, 
    {"editInfo": 
      {"createdBy": "testname", 
       "createdDate": 1503137795000, 
       "modifiedBy": "testname", 
       "modifiedDate": 1503137795000}, 
     "charInfo": 
      {"charid": "aaaaaaaaaa", 
       "charDesc": "asdfaadsf   asdfasdf asdf", 
       "status": "ON"}
    }, 
    {"editInfo": 
      {"createdBy": "testname", 
       "createdDate": 1503137795000, 
       "modifiedBy": "testname", 
       "modifiedDate": 1503137795000}, 
     "charInfo": 
      {"charid": "abababab", 
       "charDesc": "abababababab", 
       "status": "ON"}
    }
  ]} 

I am ok converting in 2 like separately for createdDate and modifiedDate. But Im looking for one line solution