Update last_activity_date with random times

randomize_time_field

def make_random_time
  date1 = Time.new
  date2 = Time.new - 50000000 # Beginning of time range
  Time.at((date2.to_f - date1.to_f) * rand + date1.to_f).to_s
end

contacts = Contact.where(...)

contacts.each { |contact| contact.update_attribute(:last_activity_date, make_random_time) }