time parsing improvements

[embray]

Still more work is to be done on time parsing (possibly worth splitting into subtasks):

• Not all time formats are parsed yet
• Handling a time array value is not supported yet at all (should maybe be noted in the docs)
  • Here need to consider a good story for the API in terms of how to handle types like this that can be a scalar or an array.
• No user documentation for times yet (just in the header)