Time parsing bug in ambient observation output

There is a bug where date times are not parsed correctly when converting from POSIXct back to character when writing output hdf5 files. (Output date times end up being: %Y-%m-%dT00:00:000Z, with %H:%M:%S clearly not being parsed correctly.)

Locate the POSIXct-to-character conversion used when writing ambient observation output to HDF5 files, then reproduce the reported timestamp formatting. Verify that output includes the intended date and hour-minute-second components rather than a midnight value with an extra zero, and add or run a regression check if the package has one.

Written by the indexing model from the issue text.