You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: schedule.rb
    path of file: ./repos/ice_cube/lib/ice_cube
    
    the code of the file until where you have to start completion: require "yaml"

module IceCube
  class Schedule
    extend Deprecated

    # Get the start time
    at
    
    def initialize(start_time = nil, options = {})
      self.start_time = start_time || TimeUtil.now
      self.end_time = self.start_time + options[:duration] if options[:duration]
      self.end_time = options[:end_time] if options[:end_time]
      @all_recurrence_rules = []
      @all_exception_rules = []
      yield self if block_given?
    end