time   = Time.parse('Tue, 03 Feb 2015 22:32:11 MSK +03:00')
_begin = time.beginning_of_day
_end   = time.end_of_day
target = '/tmp/5k_promos_3_4_2015.txt'

File.open(target, "w+") do |f|
  Promocode.where(['generated_at >= ?', _begin]).where(['generated_at <= ?', _end]).each do |promo|
    f.puts(promo.code)
  end
end