class Time

def end_of_day

Returns a new Time representing the end of the day, 23:59:59.999999 (.999999999 in ruby1.9) 
def end_of_day
  change(
    :hour => 23,
    :min => 59,
    :sec => 59,
    :usec => Rational(999999999, 1000)
  )
end