Time difference between two timestamps in Apex

Subtracting two date values in Oracle results in number of DAYS. Therefore, you'd have to do some math in order to get hours (or minutes). Here's an example:

col diff_days format 90D00000
col diff_hours format 90D00000
col diff_minutes format 90D00000
with test as (select to_date('29.12.2017 16:05', 'dd.mm.yyyy hh24:mi') d_order,
                       to_date('29.12.2017 16:39', 'dd.mm.yyyy hh24:mi') d_now
                from dual)
   select
      d_now - d_order              diff_days,
    (d_now - d_order) * 24        diff_hours,
    (d_now - d_Order) * (24 * 60) diff_minutes
   from test;

OUTPUT
DIFF_DAYS DIFF_HOURS DIFF_MINUTES
--------- ---------- ------------
  0,02361    0,56667     34,00000