Alvaro Herrera <alvherre(at)dcc(dot)uchile(dot)cl> writes:
> ... ISTM the format string
> should allow unconverted literals, so you would use
> SELECT to_char( INTERVAL '43 hours 20 minutes', 'MI min' );
... which to_char can do already, IIRC. The rewrite should define a new
set of format substitution codes, but not otherwise change the behavior
of to_char.
regards, tom lane