D7 Why I cannot just copy a template file from a module to my custom theme to override it?
Create tpl file for field field--field-name.tpl.php. place it to your theme.


  if Field name is: field_page_photos
  then File name will: field--field-page-photos.tpl.php


copy sites/all/modules/timefield/theme/timefield.tpl.php code to above tpl file.
make changes and clear cache.