They work like your sub. The billing for retainers occurs at the same time as your sub. If you cancel it, for example, 7 days before your sub is up, you'll still have them for those 7 days until the next billing occurs. If you buy one 15 days into your month you only pay for the remaining 15 days and then pay the full $2 the next time you're billed for your sub (in other words you don't lose money by buying them partway into a month or whatever your billing cycle is). If you decide to cancel a retainer, it will stay there suspended along with any items and gil you have on it, so it won't be lost completely, you'll just have to pay for the extra retainer again to use it and get any items or gil you leave on them. Hope that makes sense ^_^' if it doesn't, let me know, and I'll try to explain it better.