Oracle Scheduler - Oracle 10g/11g Data and Database Management Utilities - page 207

BY{ * } clause Syntax and Definition
BYMONTHDAY BYMONTHDAY = {[minus] 1, 2, ..., 31}
The month day is the regular calendar day, it starts the first day of the
month and it may end on the 28th, 29th, 30th, or 31st day of the month,
depending on the specific month and year. If the month day includes
a minus sign, this means that it counts backwards from the last day of
the month, so a convenient way to refer to the last day of the month is
with the expression BYMONTHDAY= -1.

BYDAY BYDAY = {[minus] [weekDayNum] MON, TUE, ... SUN}

weekDayNum = {1 .. 53} (yearly) | {1 .. 5} (monthly)
The day refers to the week day ranging from MON to SUN, and the
weekDayNum stands for the number of the week , which will span
from 1 to 53 (in a yearly frequency) or from 1 to 5 (in a monthly
frequency). So the 33rd Wednesday of the year can be expressed as:
FREQ='YEARLY'; BYDAY = 33 WED
Meanwhile the third Thursday of the month can be expressed as:
FREQ='MONTHLY'; BYDAY = 3 THU
If the BYDAY clause is preceded by the minus sign it means it will be
counted backwards, so if you want to represent the last Friday of the
year then you would use:
FREQ='YEARLY'; BYDAY = -1 FRI

BYHOUR BYHOUR = {0, 1, ... 23}

This specifies the hour in a 24 hour format ranging from 0 (12:00 a.m.)
to 23 (11 p.m.).

BYMINUTE = {0, 1, ... 59}
This specifies the minutes past the hour the task will be scheduled,
it ranges from 0 to 59. Its meaning is straightforward.

BYMINUTE

BYSECOND BYSECOND = {0, 1, ... 59}

This specifies the seconds past the minute the task will be scheduled,
it ranges from 0 to 59. Its meaning is straightforward.