readNWISmeas error
Created by: dlorenz-usgs
Old measurement data do not always have the time in the measurement_dt field. On conversion to POSIXct, those data result in NA, which makes them useless and no way to recover the original dates.
I suggest inserting a new column measurement_tm that contains any text after the 10-character data in _dt and converting the _dt to class Date. Then you can append the DateTime column if you want to try to convert as POSIXct.