If it's any consolation my bank pays off my credit card every 30 days. When I signed up the credit card would get payed on the 1st of the month. Over the years that date has drifted to now be the 20th. So even the big players haven't solved this recurring payment problem.
I still think that offering "every N days" and "Nth day of the month" would cover 99% of use-cases. The big problem I ran into was when my credit-card expired, PayPal paid a recurring bill late as it had to do an "e-cheque" that had a long delay on it. So the payment happened late.
The WTF happened the next month, after I fixed the credit card issue - every future bill had the same long delay on it. Somehow their "Pxtl pays on X day of the month" had gotten shifted. So I was getting late notifications every month.
