class DateTime

def seconds_since_midnight

DateTime.new(2012, 8, 29, 23, 59, 59).seconds_since_midnight # => 86399
DateTime.new(2012, 8, 29, 12, 34, 56).seconds_since_midnight # => 45296
DateTime.new(2012, 8, 29, 0, 0, 0).seconds_since_midnight # => 0

Returns the number of seconds since 00:00:00. 
def seconds_since_midnight
  sec + (min * 60) + (hour * 3600)
end