gem 'has_duration'

create_table :users do |t|
  t.string :contact_every, null: false
  t.string :bathtub_tolerance
end

class User < ActiveRecord::Base
  has_duration :contact_every
  # Has duration does not validate presence, you have to do that yourself.
  validates :contact_every, presence: true
  has_duration :bathtub_tolerance
end

user = User.create!(contact_every: 1.year, bathtub_tolerance: 30.minutes)
puts 'that must be a record' if customer.bathtub_tolerance > 3.hours
puts "If contacted today, next contact would be made on #{user.contact_every.from_now}"