[Remind-Fans] N-day period reminders counting from specific date

[Matous Jan Fialka]

Hello.

I have a regular payment I have to pay in 30-day period starting
from a specific date I first payed it. I would like to be reminded
3 days before the date. How do I write such remind rule?

Thank you for your ideas and the great program!
Sincerely,

-- 
mjf