# File lib/rufus/sc/rtime.rb, line 322
  def Rufus.at_to_f (at)

    # TODO : use chronic if present

    at = Rufus::to_ruby_time(at) if at.is_a?(String)
    at = Rufus::to_gm_time(at) if at.is_a?(DateTime)
    #at = at.to_f if at.is_a?(Time)
    at = at.to_f if at.respond_to?(:to_f)

    raise ArgumentError.new(
      "cannot determine 'at' time from : #{at.inspect}"
    ) unless at.is_a?(Float)

    at
  end