Time ranges are incorrectly guessed as timestamps

We have data files containing time ranges, eg ``10:00-12:00``. When we upload these, the type guessing incorrectly calls them timestamps, but of course they aren't really timestamps and can't be successfully parsed as such (because they contain hyphens). Which results in an error:

INFO [ckan.controllers.api] Validation error (Action API): "{'message': 'The data was invalid (for example: a numeric value is out of range or was inserted into a text field).', '__type': 'Validation Error'}"