PostgreSQL: format interval as minutes

When I subtract timestamps, the interval is in form DD:HH:MM:SS. How can I convert it all to minutes without extracting days and hours and multiplication/addition? I'm looking for a single function which I can substitute for date_part in this query so that it returns 65:

select date_part('minutes', '65 minutes'::interval);

Context: I need to know how many minutes have passed since given timestamp.

SELECT EXTRACT(EPOCH FROM '2 months 3 days 12 hours 65 minutes'::INTERVAL)/60;

seems to work.

WARNING: "seems" is the key word.

As a previous answer points out, the trick is to convert the interval to an "epoch", that is, an absolute number of seconds, and then divide appropriately for absolute numbers of other units.

Sone years ago, I wrote an interval_convert function which generalises this to most of the arguments accepted by date_part, assuming that a month is 30 days, and a year is 365.25 days.

Feel free to use and modify as you see fit:

CREATE FUNCTION 
    interval_convert(in_unit text, in_interval interval) 
    RETURNS double precision
AS $FUNC$
    SELECT
        EXTRACT(
            EPOCH FROM
            $2 -- in_interval 
        )
        /
        -- Slightly lazy way of allowing both singular and plural
        --  has side effect that 'centurie' and 'centurys' are accepted
        --  but otherwise behaves similarly to DATE_TRUNC
        CASE TRIM(TRAILING 's' FROM LOWER(
            $1 -- in_unit
        ))
            WHEN 'microsecond'  THEN 0.000001 
            WHEN 'millisecond'  THEN 0.001
            WHEN 'second'       THEN 1
            WHEN 'minute'       THEN 60
            WHEN 'hour'         THEN 3600
            WHEN 'day'          THEN 86400
            WHEN 'week'         THEN 604800
            WHEN 'month'        THEN 2592000 -- 30 days
            -- WHEN 'quarter'      THEN -- Not supported
            WHEN 'year'         THEN 31557600 -- 365.35 days
            WHEN 'decade'       THEN 315576000
            WHEN 'century'      THEN 3155760000
            WHEN 'centurie'     THEN 3155760000
            WHEN 'millennium'   THEN 31557600000
            WHEN 'millennia'    THEN 31557600000
        END
$FUNC$
    LANGUAGE sql 
    IMMUTABLE 
    RETURNS NULL ON NULL INPUT;