Map them to a single day, so '30 hours' is 'AM'.

Have to_char(interval) and to_char(time) use "HH", "HH12" as 12-hour
intervals, rather than bypass and print the full interval hours.  This
is neeeded because to_char(time) is mapped to interval in this function.
Intervals should use "HH24", and document suggestion.

Allow "D" format specifiers for interval/time.