class Rufus::Scheduler::RepeatJob

def first_at=(first)
  @first_at = Rufus::Scheduler.parse_to_time(first)
  raise ArgumentError.new(
    "cannot set first[_at|_in] in the past: " +
    "#{first.inspect} -> #{@first_at.inspect}"
  ) if first != 0 && @first_at < Time.now
end