gistfile1.rb

class Show < ActiveRecord::Base
  attr_accessible :artist_tokens, :cost, :booking_url, :door_charge, :venue_id, :date, :time, :starts_at
  attr_reader :artist_tokens, :date, :time

  validate :is_time
  validate :is_date
  before_save :save_date_and_time

  has_many :performances
  has_many :artists, :through => :performances
  belongs_to :user
  belongs_to :venue

  def artist_tokens=(tokens)
    self.artist_ids = Artist.ids_from_tokens(tokens)
  end

  def date
    if @date
      @date
    else
      starts_at ? starts_at.in_time_zone(Venue.get_venue_timezone(self.venue_id)).strftime("%A, %B #{starts_at.day.ordinalize}") : ""
    end
  end

  def date=(d)
    @date = d
  end

  def time
    if @time
      @time
    else
      starts_at ? starts_at.in_time_zone(Venue.get_venue_timezone(self.venue_id)).strftime("%l:%M %p") : ""
    end
  end

  def time=(t)
    @time = t
  end
    
private

  def is_time
    errors.add(:time, 'must be a valid time') if ((DateTime.parse(@time) rescue ArgumentError) == ArgumentError)
  end

  def is_date
    errors.add(:date, 'must be a valid date') if ((DateTime.parse(@date) rescue ArgumentError) == ArgumentError)
  end
  
  def save_date_and_time
    time_zone = Venue.get_venue_timezone(venue_id)
    self.starts_at = ActiveSupport::TimeZone[time_zone].parse(@date + " " + @time)
  end

end

Line 36 should probably use the instance variables, rather than the getter method:

starts_at = Chronic.parse(@date + @time)