methods in_time

On the subject of "why isn't this in Ruby already?". I've written up a set of conversion methods that I felt sure were there already, except that I couldn't find them anywhere.

class Numeric
  # assumes i am expressed in seconds - converts me to minutes
  def in_minutes
    self / 60
  end
  # assumes i am expressed in seconds - converts me to hours
  def in_hours
    self / 3600
  end
  # assumes i am expressed in seconds - converts me to days
  def in_days
    self / (3600 * 24)
  end
end

So now I can do things like: 3600.in_hours, but also the more useful: (prevTime - Time.now).in_days