dc.coverage.temporal is supposed to be of type DCMI Period, which holds several fields two of which are datetimes. I don't see any way to express this as a single input field. Such values can be stored as DCSV strings, but I think submitters would welcome a little support in correctly entering such complex values.
We could put up a pair of 'date' structures on the page and condense the field content to a single string value.
This also has implications for the DataCite and EZID IdentifierProviders, since one might wish to submit intervals as the DataCite field <date dateType='dateCollected'/>, which is of type RKMS-ISO8601 (a different string format). I might suggest making an Interval class that holds broken-down intervals as a pair of Date-ish objects and has methods to encode and decode both DCMI Period and RKMS-ISO8601 strings.