The easiest way to monitor the inserts is to create a "before insert"
trigger, in combination with an audit table. In that audit table,
simply insert the time, and possibly additional info (like the user)
of that insert. No data dictionary view will give you that info.
To see how much space a segment occupies, use DBMS_SPACE.FREE_BLOCKS
(for a manually-managed segment) or DBMS_SPACE.SPACE_USAGE (for an
automatically-managed segment). For a specific row, you'll need to add
the info of each column data.
It would be easier to answer your question if you provided more
details such as your Oracle version, as Oracle's functionality changes
significantly from version to version.
Daniel