By default, oracle date subtraction returns a result in # of days.
So just multiply by 24 to get # of hours, and again by 60 for # of minutes.
Example:
select
round((second_date - first_date) * (60 * 24),2) as time_in_minutes
from
(
select
to_date('01/01/2008 01:30:00 PM','mm/dd/yyyy hh:mi:ss am') as first_date
,to_date('01/06/2008 01:35:00 PM','mm/dd/yyyy HH:MI:SS AM') as second_date
from
dual
) test_data